
Glass Ql\ 

Book 



Cojpghl N°. 






COFYRKWIT DEPOSIT. 



ELEMENTARY BOTANY 



GEORGE FRANCIS ATKINSON, Ph.B. 

Professor of Botany in Cornell University 



THIRD EDITION, REVISED 




NEW YORK 

HENRY HOLT AND COMPANY 

J 9°5 



"-AS 7 



(Opies fliectJiveu 



Copyright, 1898, 1905 



HENRY HOLT AND COMPANY 



ROBERT DRUMMOKD, TRINTER, NSW YORK 



PREFACE. 

The present book is the result of a revision and elaboration 
of the author's " Elementary Botany," New York, 1898. The 
general plan of the parts on physiology and general morphology 
remains unchanged. A number of the chapters in the physio- 
logical part are practically untouched, while others are thoroughly 
revised and considerable new matter is added, especially on the 
subjects of nutrition and digestion. The principal chapters 
on general morphology are unchanged or only slightly modified, 
the greatest change being in a revision of the subject of the 
morphology of fertilization in the gymnosperms and angiosperms 
in order to bring this subject abreast of the discoveries of the 
past few years. One of the greatest modifications has been in 
the addition of chapters on the classification of Ihe algae and 
fungi with studies of additional examples for the benefit of those 
schools where the time allowed for the first year's course makes 
desirable the examination of a broader range of representative 
plants. The classification is also carried out with greater definite- 
ness, so that the regular sequence of classes, orders, and families 
is given at the close of each of the subkingdoms. Thus all the 
classes, all the orders (except a few in the algae), and many of 
the families, are given for the algae, fungi, mosses, liverworts, 
pteridophytes, gymnosperms, and angiosperms. 

But by far the greatest improvement has been in the complete 
reorganization, rewriting, and elaboration of the part dealing 
with ecology, which has been made possible by studies of the 
past few years, so that the subject can be presented in a more 
logical and coherent form. As a result the subject-matter of 

iii 



IV PREFACE. 

the book falls naturally into three parts, which may be passed 
in review as follows: 

Part I. Physiology. This deals with the life processes of plants, 
as absorption, transpiration, conduction, photosynthesis, nutrition, 
assimilation, digestion, respiration, growth, and irritability. 
Since protoplasm is fundamental to all the life work of the 
plant, this subject is dealt with first, and the student is led 
through the study of, and experimentation with, the simpler as 
well as some of the higher plants, to a general understanding 
of protoplasm and the special way in which it enables the plant 
to carry on its work and to adjust itself to the conditions of its 
existence. This study also serves the purpose of familiarizing 
the pupil with some of the lower and unfamiliar plants. 

Some teachers will prefer to begin the study with general 
morphology and classification, thus studying first the represen- 
tatives of the great groups of plants, and others will prefer to 
dwell first on the ecological aspects of vegetation. This can 
be done in the use of this book by beginning with Part II or 
with Part III. 

But the author believes that morphology can best be com- 
prehended after a general study of fife processes and functions 
of the different parts of plants, including in this study some of 
the lower forms of plant life where some of these processes can 
more readily be observed. The pupil is then prepared for a 
more intelligent consideration of general and comparative 
morphology and relationships. Even more important is a first 
study of physiology before taking up the subject of ecology. 
The great value to be derived from a study of plants in their 
relation to environment lies in the ability to interpret the dif- 
ferent states, conditions, behavior, and associations of the plant, 
and for this physiology is indispensable. It is true that a con- 
siderable measure of success can be obtained by a good teacher 
in beginning with either subject, but the writer believes that 
measure of success would be greater if the subjects were taken 
up in the order presented here. 

Part II. Morphology and lije history of representative plants. 



PREFA CE. V 

This includes a rather careful study of representative examples 
among the algae, fungi, liverworts, mosses, ferns and their 
allies, gymnosperms and angiosperms, with especial emphasis 
on the form of plant parts, and a comparison of them in the 
different groups, with a comparative study of development, 
reproduction, and fertilization, rounding out the work with a 
study of life histories and noting progression and retrogression 
of certain organs and phases in proceeding from the lower to the 
higher plants. Thus, in the algae a first critical study is made 
of four examples which illustrate in a marked way progressive 
stages of the plant body, sexual organs, and reproduction. Addi- 
tional examples are then studied for the purpose of acquiring a 
knowledge of variations from these types and to give a broader 
basis for the brief consideration of general relationships and 
classification. 

A similar plan is followed in the other great groups. The 
processes of fertilization and reproduction can be most easily 
observed in the lower plants like the algae and fungi, and this 
is an additional argument in favor of giving emphasis to these 
forms of plant life as well as the advantage of proceeding logic- 
ally from simpler to more complex forms. Having also learned 
some of these plants in our study of physiology, we are following 
another recognized rule of pedagogy, i.e., proceeding from 
known objects to unknown structures and processes. Through 
the study of the organs of reproduction of the lower plants and 
by general comparative morphology we have come to an under- 
standing of tho morphology of the parts of the flower, and of 
the true sexual organs of the seed plants, and no student can 
hope to properly interpret the significance of the flower, or the 
sexual organs of the seed plants who neglects a careful study 
of the general morphology of the lower plants. 

Part III. Plant members in relation to environment. This part 
deals with the organization of the plant body as a whole in its 
relation to environment, the organization of plant tissues with 
a discussion of the principal tissues and a descriptive synopsis of 
the same. This is followed by a complete study from a biological 



VI PREFACE. 

standpoint of the different members of the plant, their special 
function and their special relations to environment. The stem, 
root, leaf, flower, etc., are carefully examined and their ecological 
relations pointed out. This together with the study of physiology 
and representatives in the groups of plants forms a thorough 
basis for pure plant ecology, or the special study of vegetation 
in its relation to environment. 

There is a study of the factors of environment or ecological 
factors, which in general are grouped under the physical, climatic, 
and biotic factors. This is followed by an analysis of vegeta- 
tion forms and structures, plant formations and societies. Then 
in order are treated briefly forest societies, prairie societies, 
desert societies, arctic and alpine societies, aquatic societies, and 
the special societies of sandy, rocky, and marshy places. 

Acknowledgments. The author wishes to express his grate- 
fulness to all those who have given aid in the preparation of this 
work, or of the earlier editions of Elementary Botany; to his 
associates, Dr. E. J. Durand, Dr. K. M. Wiegand, and Professor 
W. W. Rowlee, of the botanical department, and to Professor 
B. M. Duggar of the University of Missouri, Professor J. C. 
Arthur of Purdue University, and Professor W. F. Ganong of 
Smith College, for reading one or more portions of the text; 
as well as to all those who have contributed illustrations. 

Illustrations. The large majority of the illustrations are new 
(or are the same as those used in earlier editions of the author's 
Elementary Botany) and were made with special reference to 
the method of treatment followed in the text. Many of the 
photographs were made by the author. Others were contributed 
by Professor Rowlee of Cornell University; Mr. John Gifford 
of New Jersey; Professor B. M. Duggar, University of Missouri; 
Professor C. E. Bessey, University of Nebraska; Dr. M. B. Howe, 
New York Botanical Garden; Mr. Gifford Pinchot, Chief of 
the Bureau of Forestry; Mr. B. T. Galloway, Chief of the 
Bureau of Plant Industry; Professor Tuomey of Yale University; 
and Mr. E. H. Harriman, who through Dr. C. H. Merriam 
of the National Museum allowed the use of several of his copy- 



PREFA CE . Vll 

righted photographs from Alaska. To those who have con- 
tributed drawings the author is indebted as follows : to Professor 
Margaret C. Ferguson, Wellesley College; Professor Bertha 
Stoneman of Huguenot College, South Africa; Mr. H. Hassel- 
bring of Chicago; Dr. K. Miyake, formerly of Cornell University 
and now of Doshisha College, Japan; and Professors Ikeno 
and Hirase of the Tokio Imperial University. The author 
is also indebted to Ginn & Co., Boston, for the privilege to 
use from his "First Studies of Plant Life" the following figures: 
28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103, 422-426, 429, 
43°> 438-440, 443> 444, 448, 449, 452, 47 2 ~475- A few others 
are acknowledged in the text. 

Cornell University, April, 1905. 



TABLE OF CONTENTS. 

PART I. PHYSIOLOGY. 
CHAPTER I. 

PAGE 

Protoplasm i 

CHAPTER II. 
Absorption, Diffusion, Osmose 13 

CHAPTER III. 
How Plants Obtain Water 22 

CHAPTER IV. 
Transpiration, or the Loss of Water by Plants 35 

CHAPTER V. 
Path of Movement of Water in Plants 48 

CHAPTER VI. 
Mechanical Uses of Water 56 

CHAPTER VII. 

Starch and Sugar Formation 60 

1. The Gases Concerned 60 

2. Where Starch is Formed 64 

3. Chlorophyll and the Formation of Starch 67 

CHAPTER VIII. 

Starch and Sugar Concluded; Analysis of Plant Substance 73 

1. Translocation of Starch 73 

2. Sugar, and Digestion of Starch. 75 

3. Rough Analysis of Plant Substance 79 

ix 



X TABLE OF CONTENTS. 

CHAPTER IX. 

PAGE 

How Plants Obtain their Food, 1 81 

i. Sources of Plant Food 81 

2. Parasites and Saprophytes 83 

3. How Fungi Obtain their Food 86 

4. Mycorhiza 91 

5. Nitrogen-gatherers 92 

6. Lichens 93 

CHAPTER X. 

How Plants Obtain their Food, II 97 

Seedlings, 97. Digestion, 107. Assimilation 109 

CHAPTER XL 
Respiration no 

CHAPTER XII. 
Growth 118 

CHAPTER XIII. 
Irritability 125 

PART II. MORPHOLOGY AND LIFE HISTORY 
OF REPRESENTATIVE PLANTS. 

CHAPTER XIV. 
Spirogyra 136 

CHAPTER XV. 

VAUCHERIA : 142 

CHAPTER XVI. 
OEdogonium 147 

CHAPTER XVII. 

COLEOCH^ETE 153 

CHAPTER XVIII. 

Classification and Additional Studies of the Alg,e 158 

CHAPTER XIX. 
Fungi : Mucor and Saprolegnja ,......,..,...,.. 177 



TABLE OF CONTENTS. Xl 

CHAPTER XX. 

PAGE 

Fungi Continued (" Rusts " Uredineae) 187 

CHAPTER XXI. 
The Higher Fungi 195 

CHAPTER XXII. 
Classification of the Fungi 213 

CHAPTER XXIII. 

Liverworts (Hepaticae) 222 

Riccia, 222. Marchantia 226 

CHAPTER XXIV. 

Liverworts Continued 231 

Sporogonium of Marchantia 231 

Leafy-stemmed Liverworts 236 

The Horned Liverworts 240 

Classification of the Liverworts 242 

CHAPTER XXV. 

Mosses (Musci) 243 

Classification of Mosses 248 

CHAPTER XXVI. 
Ferns 251 

CHAPTER XXVII. 

Ferns Continued 262 

Gametophyte of Ferns 262 

Sporophyte 268 

CHAPTER XXVIII. 
Dimorphism of Ferns 273 

CHAPTER XXIX. 
Horsetails. ............ 280 

CHAPTER XXX. 
Club-mosses. 284 

CHAPTER XXXI. 
Quillworts (Isoetes) 289 



xil TABLE OF CONTENTS. 

CHAPTER XXXII. 

PAGE 

Comparison of Ferns and their Relatives 292 

Classification of the Pteridophytes 295 

CHAPTER XXXIII. 
Gynmosperms 297 

CHAPTER XXXIV. 
Further Studies on Gymnosperms 311 

CHAPTER XXXV. 
Morphology of the Angiosperms: Trillium; Dent aria 318 

CHAPTER XXXVI. 
Gametophyte and Sporophyte of Angiosperms 325 

CHAPTER XXXVII. 

Morphology of the Nucleus and Significance of Gametophyte 
and Sporophyte 340 

PART III. PLANT MEMBERS IN RELATION 
TO ENVIRONMENT. 

CHAPTER XXXVIII. 

The Organization of the Plant 349 

I. Organization of Plant Members 349 

II. Organization of Plant Tissues 356 

CHAPTER XXXIX. 

The Different Types of Stems 365 

I. Erect Stems 365 

II. Creeping, Climbing, and Floating Stems 369 

III. Specialized Shoots and Shoots for Storage of Food 372 

IV. Annual Growth and Winter Protection of Shoots and Buds. . . 374 

CHAPTER XL. 

Foliage Leaves 3%3 

I. General Form and Arrangement of Leaves 383 

II. Protective Modifications of Leaves .... 392 

III. Protective Positions 395 

IV. Relation of Leaves to Light 397 

V. Leaf Patterns 404 



TABLE OF CONTENTS. Xill 

CHAPTER XLI. 

PAGE 

The Root 410 

I. Function of Roots 410 

II. Kinds of Roots 415 

CHAPTER XLII. 

The Floral Shoot 419 

I. The Parts of the Flower 419 

II. Kinds of Flowers 421 

III. Arrangement of Flowers, or Mode of Inflorescence 426 

CHAPTER XLIII. 

POLLLNATION 433 

CHAPTER XLIV. 

The Fruit 450 

I. Parts of the Fruit 450 

II. Indehiscent Fruits 451 

III. Dehiscent Fruits 452 

IV. Fleshy and Juicy Fruits 454 

V. Reinforced, or Accessory, Fruits 455 

VI. Fruits of Gymnosperms 456 

VII. "Fruit" of Ferns, Mosses, etc 457 

CHAPTER XLV. 
Seed Dispersal 458 

CHAPTER XLVI. 
Vegetation in Relation to Environment 464 

CHAPTER XLVII. 
Classification of Angiosperms 487 



Index 



503 



PART I. 

PHYSIOLOGY. 

CHAPTER I. 

PROTOPLASM.* 

1. In the study of plant life and growth, it will be found 
convenient first to inquire into the nature of the substance 
which we call the living material of plants. For plant growth, 
as well as some of the other processes of plant life, are at bottom 
dependent on this living matter. This living matter is called in 
gen e ral protoplasm . 

2. In most cases protoplasm cannot be seen without the 
help of a microscope, and it will be necessary for us here to em- 
ploy one if we wish to see protoplasm, and to satisfy ourselves 
by examination that the substance we are dealing with is 
protoplasm. 

3. We shall find it convenient first to examine protoplasm in 
some of the simpler plants ; plants which from their minute size 
and simple structure are so transparent that when examined with 
the microscope the interior can be seen. 

For our first study let us take a plant known as spirogyra, 
though there are a number of others which would serve the pur- 
pose quite as well, and may quite as easily be obtained for 
study. 

*For apparatus, reagents, collection and preservation of material, etc., see 
Appendix. 



PHYSIOLOGY. 



Protoplasm in spirogyra. 

4. The plant spirogyra. — This plant is found in the water 
of pools, ditches, ponds, or in streams of slow-running water. 
It is green in color, and occurs in loose mats, usually floating 
near the surface. The name "pond-scum" is sometimes given 
to this plant, along with others which are more or less closely 
related. It is an alga, and belongs to a group of plants known 
as algcB. If we lift a portion of it from the water, we see that 
the mat is made up of a great tangle of green silky threads. 
Each one of these threads is a plant, so that the number con- 
tained in one of these floating mats is very great. 

Let us place a bit of this thread tangle on a glass slip, and 
examine with the microscope and we will see certain things about 
the plant which are peculiar to it, and which enable us to dis- 
tinguish it from other minute green water plants. We shall 
also wish to learn what these peculiar parts of the plant are, in 
order to demonstrate the protoplasm in the plant.* 

5. Chlorophyll bands in spirogyra. — We first observe the 
presence of bands ; green in color, the edges of which are 
usually very irregularly notched. These bands course along in 
a spiral manner near the surface of the thread. There may be 
one or several of these spirals, according to the species which 
we happen to select for study. This green coloring matter of 
the band is chlorophyll, and this substance, which also occurs in 
the higher green plants, will be considered in a later chapter. 
At quite regular intervals in the chlorophyll band are small 
starch grains, grouped in a rounded mass enclosing a minute 
body, the pyrenoid, which is peculiar to many algae. 

6. The spirogyra thread consists of cylindrical cells end to 
end. — Another thing which attracts our attention, as we examine 
a thread of spirogyra under the microscope, is that the thread is 

"* If spirogyra is forming fruit some of the threads will be lying parallel in 
pairs, and connected with short tubes. In some of the cells there will be 
found rounded or oval bodies known as zygospores. These may be seen in 
fig. 86, and will be described in another part of the book. 



PROTOPLASM. 



made up of cylindrical segments or compartments placed end to 
end. We can see a distinct separating line be- 
tween the ends. Each one of these segments or 
compartments of the thread is a cell, and the 
boundary wall is in the form of a cylinder with 
closed ends. 

7. Protoplasm. — Having distinguished these 
parts of the plant we can look for the protoplasm. 
It occurs within the cells. It is colorless (i.e., 
hyaline) and consequently requires close observa- 
tion. Near the center of the cell can be seen a 
rather dense granular body of an elliptical or 
irregular form, with its long diameter transverse 
to the axis of the cell in some species ; or trian- 
gular, or quadrate in others. This is the nucleus. 
Around the nucleus is a granular layer from which 
delicate threads of a shiny granular substance 
radiate in a starlike manner, and terminate in the 
chlorophyll band at one of the pyrenoids. A 
granular layer of the same substance lines the 
inside of the cell wall, and can be seen through 
the microscope if it is properly focussed. This 
granular substance in the cell is protoplasm. 

8. Cell-sap in spirogyra. — The greater part of 
the interior space of the cell, that between the 
radiating strands of protoplasm, is occupied by 
a watery fluid, the "cell -sap." 

9. Reaction of protoplasm to certain reagents. 
— We can employ certain tests to demonstrate 
that'this granular substance which we have seen 
is protoplasm, for it has been found, by repeated Flg * *' 
experiments with a great many kinds of plants, gyra/showingC 
that protoplasm gives a definite reaction in re- ban'd, c Seus, 
sponse to treatment with certain substances called pksm, 5 °and Pr °t]?e 
reagents. Let us mount a few threads of the ^"to^sm.*^ 
spirogyra in a drop of a solution of iodine, and observe the 



PHYSIO LOG Y. 



results with the aid of the microscope. The iodine gives a 
yellowish-brown color to the protoplasm, and it can be more 
distinctly seen. The nucleus is also much more prominent 
since it colors deeply, and we can perceive within the nucleus 
one small rounded body, sometimes more, the nucleolus. The 
iodine here kills and stains the protoplasm. The proto- 
plasm, however, in a living condition will resist for a time some 

other reagents, 
as we shall see 
if we attempt 
to stain it with 
a one per cent 
aqueous solu- 
tion of a dye 
known as eosin. 
Let us mount a 
few living 
threads in such 
a solution of 
eosin, and after 
a time wash off 

i-i atment 4.u p ^j.,^ Thf^ 
with alcohol and iodine. ine bldlll. 1 ne 

protoplasm remains uncolored. Now let us place these threads 
for a short time, two or three minutes, in strong alcohol, which 
kills the protoplasm. Then mount them in the eosin solution. 
The protoplasm now takes the eosin stain. After the proto- 
plasm has been killed we note that the nucleus is no longer 
elliptical or angular in outline, but is rounded. The strands of 
protoplasm are no longer in tension as they were when alive. 

10. Let us now take some fresh living threads and mount 
them in water. Place a small drop of dilute glycerine on the 
slip at one side of the cover glass, and with a bit of filter paper 
at the other side draw out the water. The glycerine will flow 
under the cover glass and come in contact with the spirogyra 
threads. Glycerine absorbs water promptly. Being in contact 
with the threads it draws water out of the cell cavity, thus cans- 




Fig. 2. 

Cell of spirogyra before treat 

ment with iodine. 



Fig. 3- 
Cell of spirogyra after treatment 



PROTOPLASM. 



5 



ing the layer of protoplasm which lines the inside of the cell 
wall to collapse, and separate from the wall, drawing the 
chlorophyll band 
inward toward the 
center also. The 
wall layer of proto- 
plasm can now be 
more distinctly 
seen and its gran- 
ular character ob- 
served. 

We have thus 
employed three 
tests to demon- 
strate that this sub- 
stance with which 
we are dealing 
shows the reac- 
tions which we 
know by experi- 





Fig. 4- 

Cell of spirogyra before 



Fig. 5- 

Cells of spirogyra after treatment 

with glycerine. 



ence tO be given treatment with glycerine. 

by protoplasm. We therefore conclude that this colorless and 
partly granular, slimy substance in the spirogyra cell is proto- 
plasm, and that when we have performed these experiments, 
and noted carefully the results, we have seen protoplasm. 



11. Earlier use of the term protoplasm. — Early students of the living 
matter in the cell considered it to be alike in substance, but differing in 
density; so the term protoplasm was applied to all of this living matter. The 
nucleus was looked upon as simply a denser portion of the protoplasm, and 
the nucleolus as a still denser portion. Now it is believed that the nucleus is 
a distinct substance, and a permanent organ of the cell. The remaining por- 
tion of the protoplasm is now usually spoken of as the cytoplasm. 

In spirogyra then the cytoplasm in each cell consists of a layer which lines 
the inside of the cell wall, a nuclear layer, which surrounds the nucleus, and 
radiating strands which connect the nucleus and wall layers, thus suspending 
the nucleus near the center of the cell. But it seems best in this elementary 
Study to use the term protoplasm in its general sense. 



PHYSIOLOGY. 



Protoplasm in mucor. 

12. Let us now examine in a similar way another of the 
simple plants with the special object in view of demonstrating 
the protoplasm. For this purpose we may take one of the plants 
belonging to the group of fungi. These plants possess no 
chlorophyll. One of several species of mucor, a common 
mould, is readily obtainable, and very suitable for this study.* 

13. Mycelium of mucor. — A few days after sowing in some 
gelatinous culture medium we find slender, hyaline threads, which 
are very much branched, and, radiating from a central point, form 
circular colonies, if the plant has not been too thickly sown, as 
shown in fig. 6. These threads of the fungus form the myce- 
lium. From these characters of the plant, which we can readily 
see without the aid of a microscope, we note how different it is 
from spirogyra. 

To examine for protoplasm let us lift carefully a thin block of 
gelatine containing the mucor threads, and mount it in water on 
a glass slip. Under the microscope we see only a small portion 
of the branched threads. In addition to the absence of chlo- 
rophyll, which we have already noted, we see that the myce- 
lium is not divided at short intervals into cells, but appears 
like a delicate tube with branches, which become successively 
smaller toward the ends. 

14. Appearance of the protoplasm. — Within the tube-like 
thread now note the protoplasm. It has the same general ap- 
pearance as that which we noted in spirogyra. It is slimy, or 
semi-fluid, partly hyaline, and partly granular, the granules con- 
sisting of minute particles (the microsomes). While in mucor the 
protoplasm has the same general appearance as in spirogyra, its 
arrangement is very different. In the first place it is plainly 

* The most suitable preparations of mucor for study are made by growing 
the plant in a nutrient substance which largely consists of gelatine, or, better, 
agar-agar, a gelatinous preparation of certain seaweeds. This*, after the 
plant is sown in it, should be poured jntQ Sterjljged. shallow glass plates, 

called Petrje dishes, 



PROTOPLASM. 7 

continuous throughout the tube. We do not see the prominent 
radiations of strands around a large nucleus, but still the proto- 



jf 





Fig 6. 
Colonies of mucor. 

plasm does not fill the interior of the threads. Here and there 
are rounded clear spaces termed vacuoles, which are filled with 
the watery fluid, cell-sap. The nuclei in mucor are very mi- 
nute, and cannot be seen except after careful treatment with 
special reagents. 

15 Movement of the protoplasm in mncor. — While exam- 
ining the protoplasm in mucor we are likely to note streaming 
movements. Often a current is seen flowing slowly down one 
side of the thread, and another flowing back on the other side, 
or it may all stream along in the same direction. 

16. Test for protoplasm. — Now let us treat the threads with 
a solution of iodine. The yellowish-brown color appears which 
is characteristic of protoplasm when subject to this reagent. 



8 PHYSIOLOG Y. 

If we attempt to stain the living protoplasm with a one per 
cent aqueous solution of eosin it resists it for a time, but if we 
first kill the protoplasm with strong alcohol, it reacts quickly to 
the application of the eosin. If we treat the living threads 
with glycerine the protoplasm is contracted away from the wall, 
as we found to be the case with spirogyra. While the color, 




Fig. 7. 
Thread of mucor, showing protoplasm and vacuoles. 

form and structure of the plant mucor is different from spiro 
gyra, and the arrangement of the protoplasm within the plant 
is also quite different, the reactions when treated by certain re- 
agents are the same. We are justified then in concluding that 
the two plants possess in common a substance which we call 
protoplasm. 

Protoplasm in nitella. 

17. One of the most interesting plants for the study of one remarkable 
peculiarity of protoplasm is Nitella. This plant belongs to a small group 
known as stoneworts. They possess chlorophyll, and, while they are still 
quite simple as compared with the higher plants, they are much higher in the 
scale than spirogyra or mucor. 

18. Form of nitella. — A common species of nitella is Nitella Jlexilis. 
It grows in quiet pools of water. The plant consists of a main axis, in the 
form of a cylinder. At quite regular intervals are whorls of several smaller 
thread-like outgrowths, which, because of their position, are termed " leaves," 
though they are not true leaves. These are branched in a characteristic fash- 
ion at the tip. The main axis also branches, these branches arising in the axil 
of a whorl, usually singly. The portions of the axis where the whorls arise 
are the nodes. Each node is made up of a number of small cells definitely 
arranged. The portion of the axis between two adjacent whorls is an inter- 



PROTOPLASM. 9 

node. These internodes are peculiar. They consist of but a single " cell." 
and are cylindrical, with closed ends. They are sometimes 5-10 cm. long. 

19. Internode of nitella. — For the study of an internode of nitella, a 
small one, near the end, or the ends of one of the " leaves" is best suited, 
since it is more transparent. A small 
portion of the plant should be placed 
on the glass slip in water with the 
cover glass over a tuft of the branches 
near the growing end. Examined with 
the microscope the green chlorophyll bodies, which 
form oval or oblong discs, are seen to be very numer- 
ous. They lie quite closely side by side and form in 
perfect rows along the inner surface of the wall. One 
peculiar feature of the arrangement of the chlorophyll 
bodies is that there are two lines, extending from one 
end of the internode to the other on opposite sides, 
where the chlorophyll bodies are wanting. These are 
known as neutral lines. They run parallel with the 
axis of the internode, or in a more or less spiral 
manner as shown in fig. 9. 

20. Cyclosis in nitella. — The chlorophyll bodies 

are stationary on the inner surface of the wall, but 

if the microscope be properly focussed just beneath 

this layer we notice a rotary motion of particles in 

the protoplasm. There are small granules and quite 

large masses of granular matter which glide slowly 

along in one direction on a given side of the neutral 

line. If now we examine the protoplasm on the other 

side of the neutral line, we see that the movement is 

in the opposite direction. If we examine this move- lg * 

Portion of plant nitella. 
ment at the end of an internode the particles are seen 

to glide around the end from one side of the neutral line to the other. So 
that when conditions are favorable, such as temperature, healthy state of the 
plant, etc., this gliding of the particles or apparent streaming of the proto- 
plasm down one side of the " cell," and back upon the other, continues in 
an uninterrupted rotation, or cyclosis. There are many nuclei in an internode 
of nitella, and they move also. 

21. Test for protoplasm. — If we treat the plant with a solution of iodine 
we get the same reaction as in the case of spirogyra and mucor. The proto- 
plasm becomes yellowish brown. 

22. Protoplasm in one of the higher plants. — We now wish 
to examine, and test for, protoplasm in one of the higher plants. 





IO PHYSIOLOGY. 

Young or growing parts of any one of various plants — the petioles 
of young leaves, or young stems of growing plants — are suitable 
for study. Tissue from the pith of corn (Zea mays) in young 

shoots just back of the 
growing point or quite 
near the joints of older but 
growing corn stalks fur- 
Fig. 9> nishes excellent material. 
Cydosis in niteiia. If we should place part 
of the stem of this plant under the microscope we should find 
it too opaque for observation of the interior of the cells. This 
is one striking difference which we note as we pass from the low 
and simple plants to the higher and more complex ones ; not 
only in general is there an increase of size, but also in general 
an increase in thickness of the parts. The cells, instead of lying 
end to end or side by side, are massed together so that the parts 
are quite opaque. In order to study the interior of the plant 
we have selected it must be cut into such thin layers that the 
light will pass readily through them. 

For this purpose we section the tissue selected by making with 
a razor, or other very sharp knife, very thin slices of it. These 
are mounted in water in the usual way for microscopic study. In 
this section we notice that the cells are polygonal in form. 
This is brought about by mutual pressure of all the cells. The 
granular protoplasm is seen to form a layer just inside the wall, 
which is connected with the nuclear layer by radiating strands 
of the same substance. The nucleus does not always lie at the 
middle of the cell, but often is near one side. If we now apply 
an alcohol solution of iodine the characteristic yellowish-brown 
color appears. So we conclude here also that this substance is 
identical with the living matter in the other very different plants 
which we have studied. 

23. Movement of protoplasm in the higher plants. — Cer- 
tain parts of the higher plants are suitable objects for the study 
of the so-called streaming movement of protoplasm, especially 
the delicate hairs, or thread-like outgrowths, §uch as the silk of 



PROTOPLASM. II 

corn, or the delicate staminal hairs of some plants, like those of 
the common spiderwort, tradescantia, or of the tradescantias 
grown for ornament in greenhouses and plant conservatories. 

Sometimes even in the living cells of the corn plant which we 
have just studied, slow streaming or gliding movements of the 
granules are seen along the strands of protoplasm where they 
radiate from the nucleus. See note at close of this chapter. 

24. Movement of protoplasm in cells of the staminal hair of 
" spiderwort." — A cell of one of these hairs from a stamen of a 
tradescantia grown in glass houses is shown in fig. 10. The 



Fig. 10. 
Cell from stamen hair of tradescantia showing movement of the protoplasm. 

nucleus is quite prominent, and its location in the cell varies con- 
siderably in different cells and at different times. There is a 
layer of protoplasm all around the nucleus, and from this the 
strands of protoplasm extend outward to the wall layer. The 
large spaces between the strands are, as we have found in other 
cases, filled with the cell-sap. 

An entire stamen, or a portion of the stamen, having several hairs attached, 
should be carefully mounted in water. Care should be taken that the room be 
not cold, and if the weather is cold the water in which the preparation is 
mounted should be warm. With these precautions there should be little diffi- 
culty in observing the streaming movement. 

The movement is detected by observing the gliding of the 
granules. These move down one of the strands from the nucleus 
along the wall layer, and in towards the nucleus in another 
strand. After a little the direction of the movement in any one 
portion may be reversed. 

25. Cold retards the movement. — While the protoplasm is 
moving, if we rest the glass slip on a block of ice, the move- 
ment will become slower, or will cease altogether, Then if we 



12 PHYSIOLOGY. 

warm the slip gently, the movement becomes normal again. We 
may now apply here the usual tests for protoplasm. The result 
is the same as in the former cases. 

26. Protoplasm occurs in the living parts of all plants. — 

In these plants representing such widely different groups, we find 
a substance which is essentially alike in all. Though its arrange- 
ment in the cell or plant body may differ in the different plants 
or in different parts of the same plant, its general appearance 
is the same. Though in the different plants it presents, while 
alive, varying phenomena, as regards mobility, yet when killed 
and subjected to well known reagents the reaction is in general 
identical. Knowing by the experience of various investigators 
that protoplasm exhibits these reactions under given conditions, 
we have demonstrated to our satisfaction that we have seen proto 
plasm in the simple alga, spirogyra, in the common mould, 
mucor, in the more complex stonewort, nitella, and in the cells 
of tissues of the highest plants. 

27. By this simple process of induction of these facts concerning 
this substance in these different plants, we have learned an im- 
portant method in science study. Though these facts and deduc- 
tions are well known, the repetition of the methods by which they 
are obtained on the part of each student helps to form habits of 
scientific carefulness and patience, and trains the mind to logical 
processes in the search for knowledge. 

28. While we have by no means exhausted the study of protoplasm, we can, 
from this study, draw certain conclusions as to its occurrence and appearance 
in plants. Protoplasm is found in the living and growing parts of all plants. 
It is a semi-fluid, or slimy, granular, substance ; in some plants, or parts of 
plants, the protoplasm exhibits a streaming or gliding movement of the gran- 
ules. It is irritable. In the living condition it resists more or less for some 
time the absorption of certain coloring substances. The water may be with 
drawn by glycerine. The protoplasm may be killed by alcohol. When 
treated with iodine it becomes a yellowish-brown color. 

Note. In some plants, like elodea for example, it has been found that 
the streaming of the protoplasm is often induced by some injury or stimu- 
lus, while in the normal condition the protoplasm does not move, 



CHAPTER II. 

ABSORPTION, DIFFUSION, OSMOSE. 

29. We may next endeavor to learn how plants absorb 
water or nutrient substances in solution. There are several 
very instructive experiments, which can be easily performed, 
and here again some of the lower plants will be found useful. 

30. Osmose in spirogyra. — Let us mount a few threads of 
this plant in water for microscopic examination, and then draw 
under the cover glass a five per cent solution of ordinary table 
salt (NaCl) with the aid of filter paper. We shall soon see 
that the result is similar to that which was obtained when glycer- 
ine was used to extract the water from the cell -sap, and to con- 
tract the protoplasmic membrane from the cell wall. But the 
process goes on evenly and the plant is not injured. The proto- 
plasmic layer contracts slowly from the cell wall, and the move- 
ment of the membrane can be watched by looking through the 
microscope. The membrane contracts in such a way that all 
the contents of the cell are finally collected into a rounded or 
oval mass which occupies the center of the cell. 

If we now add fresh water and draw off the salt solution, 
we can see the protoplasmic membrane expand again, or move 
out in all directions, and occupy its former position against the 
inner surface of the cell wall. This would indicate that there is 
some pressure from within while this process of absorption is 
going on, which causes the membrane to move out against the 
cell wall. 

The salt solution draws water from the cell-sap. There 
is thus a tendency to form a vacuum in the cell, and the 
pressure on the outside of the protoplasmic membrane causes it 

. - i3 



H 



PHYSIOLOGY. 



to move toward the center of the cell. When the salt solution 
is removed and the thread of spirogyra is again bathed with 
water, the movement of the water is inward in 
the cell. This would suggest that there is some 
substance dissolved in the cell-sap which does not 
readily filter out through the membrane, but draws 
on the water outside. It is this which produces 
the pressure from within and crowds the mem- 
brane out against the cell wall again. 



Fig. ir. 

Spirogyra before 
placing in salt solu- 
tion. 




Fig. 13. 

Spirogyra from salt 

solution into water. 



Fig. 12. 
Spirogyra in $% salt solution. 



31. Turgescence. — Were it not for the resistance which the 
cell wall offers to the pressure from within, the delicate proto- 



ABSORPTION, DIFFUSION", OSMOSF. 



*5 



plasmic membrane would stretch to such an extent that it would 
be ruptured, and the protoplasm therefore would be killed. If 
we examine the cells at the ends of the 
threads of spirogyra we shall see in most 
cases that the cell wall at the free end is 
arched outward. 
This is brought 
about by the press- 




Fig. i 4 . 

Before treatment with salt 
solution. 

ure from within 



Fig. 15. 

After treatment with 

salt solution. 



Fig. 16. 

From salt solution placed in water. 

Figs. 14-16. — Osmosis in threads of mucor. 



upon the proto- 
plasmic m e m - 
brane which itself presses against 
the cell wall, and causes it to 
arch outward. This is beauti- 
fully shown in the case of threads 
which are recently broken. The cell wall is therefore elastic; 
it yields to a certain extent to the pressure from within, but a 
point is soon reached beyond which it will not stretch, and an 
equilibrium then exists between the pressure from within on the 
protoplasmic membrane, and the pressure from without by the 
elastic cell wall. This state of equilibrium in a cell is turges- 
cence, or such a cell is said to be turgescent, or turgid. 

32. Experiment with beet in salt and sugar solutions. — 
We may now test the effect of a five per cent salt solution on a 
portion of the tissues of a beet or carrot. Let us cut several 
slices of equal size and about ^mm in thickness. Immerse a 
few slices in water, a few in a five per cent salt solution and a 
few in a strong sugar solution. It should be first noted that all 
the slices are quite rigid when an attempt is made to bend them 
between the fingers. In the course of one or two hours or less, 



i6 



PHYSIOLOGY. 



if we examine the slices we shall find that those in water remain, 
as at first, quite rigid, while those in the salt and sugar solutions 
are more or less flaccid or limp, and readily bend by pres- 




Fig. 17. Fig. 18. Fig. 19. 

Before treatment with salt After treatment with salt From salt solution into water 
solution. solution. again. 

Figs. 17-19. — Osmosis in cells of Indian corn. 

sure between the fingers, the specimens in the salt solution, 
perhaps, being more flaccid than those in the sugar solution. 
The salt solution, we judge after our experiment with spirogyra, 






7 

Fig. 20. Fig. 21. Fig. 22. 

Rigid condition of fresh beet Limp condition after lying in Rigid again after lying again 

section. salt solution. in water. 

Figs. 20-22. — Turgor and osmosis in slices of beet. 

withdraws some of the water from the cell-sap, the cells thus 
losing their turgidity and the tissues becoming limp or flaccid 
from the loss of water. 



ABSORPTION, DIFFUSION, OSMOSE. 



17 



33. Let us now remove some of the slices of the beet from 
the sugar and salt solutions, wash them with water and then 
immerse them in fresh water. In the course of thirty minutes 
to one hour, if we examine them again, we find that they have 
regained, partly or completely, their rigidity. Here again we 
infer from the former experiment with spirogyra that the sub- 
stances in the cell-sap now draw water inward ; that is, the 
diffusion current is inward through the cell walls and the proto- 
plasmic membrane, and the tissue becomes turgid again. 

34. Osmose in the cells of the beet. — We should now make a section of the 
fresh tissue of a red colored beet for examination with the microscope, and 
treat this section with the salt solution. Here we can see that the effect of the 
salt solution is to draw water out of the cell, so that the protoplasmic mem- 




Fig. 25. 
Later stage of the same. 



Fig. 23. Fig. 24. 

Before treatment with salt After treatment with salt 
solution. solution. 

Figs. 23-25. — Cells from beet treated with salt solution to show osmosis and movement of 
the protoplasmic membrane. 

brane can be seen to move inward from the cell wall just as was observed in 
the case of spirogyra.* Now treating the section with water and removing 
the salt solution, the diffusion current is in the opposite direction, that is in- 



* We should note that the coloring matter of the beet resides in the cell- 
sap. It is in these colored cells that we can best see the movement take 
place, since the red color serves to differentiate well the moving mass from the 
cell wall. The protoplasmic membrane at several points usually clings tena- 
ciously so that at several places the membrane is arched strongly away from 
the cell wall as shown in fig. 24. While water is removed from the cell-sap, 
we note that the coloring matter does not escape through the protoplasmic 
membrane. 



18 PHYSIOLOGY. 

ward through the protoplasmic membrane, so that the latter is pressed outward 
until it comes in contact with the cell wall again, which by its elasticity soon 
resists the pressure and the cells again become turgid. 

35. The coloring matter in the cell-sap does not readily escape from the 
living protoplasm of the beet. — The red coloring matter, as seen in the sec- 
tion under the microscope, does, not escape from the cell-sap through the pro- 
toplasmic membrane . "When the slices are placed in water, the water is not 
colored thereby. The same is true when the slices are placed in the salt or 
sugar solutions. Although water is withdrawn from the cell-sap, this coloring 
substance does not escape, or if it does it escapes slowly and after a consider- 
able time. 

36. The coloring matter escapes from dead protoplasm. — If, however, we 
heat the water containing a slice of beet up to a point which is sufficient to 
kill the protoplasm, the red coloring matter in the cell-sap filters out through 
the protoplasmic membrane and colors the water. If we heat a preparation 
made for study under the microscope up to the thermal death point we can 
see here that the red coloring matter escapes through the membrane into the 
water outside. This teaches that certain substances cannot readily filter 
through the living membrane of protoplasm, but that they can filter through 
when the protoplasm is dead. A very important condition, then, for the suc- 
cessful operation of some of the physical processes connected with absorption 
in plants is that the protoplasm should be in a living condition. 

37. Osmose experiments with leaves. — We may next take the leaves of 
certain plants like the geranium, coleus or other plant, and place them in 
shallow vessels containing water, salt, and sugar solutions respectively. The 
leaves should be immersed, but the petioles should project out of the water or 
solutions. Seedlings of corn or beans, especially the latter, may also be 
placed in these solutions, so that the leafy ends are immersed. After one or 
two hours an examination shows that the specimens in the water are still 
turgid. But if we lift a leaf or a bean plant from the salt or sugar solution, 
we find that it is flaccid and limp. The blade, or lamina, of the leaf 
droops as if wilted, though it is still wet. The bean seedling also is flaccid, 
the succulent stem bending nearly double as the lower part of the stem is held ! 
upright. This loss of turgidity is brought about by the loss of water from the 
tissues, and judging from the experiments on spirogyra and the beet, we con- 
clude that the loss of turgidity is caused by the withdrawal of some of the 
water from the cell-sap by the strong salt solution. 

38. Now if we wash carefully these leaves and seedlings, which have been 
in the salt and sugar solutions, with water, and then immerse them in fresh 
water for a few hours, they will regain their turgidity. Here again we are led 
to infer that the diffusion current is now inward through the protoplasmic 
membranes of all the living cells of the leaf, and that the resulting turgidity 
of the individual cells causes the turgidity of the leaf or stem. 



ABSORPTION, DIFFUSION, OSMOSE. 



9 



\ 



t I 



39. Absorption by root hairs. — If we examine seedlings, 
which have been grown in a germinator or in the folds of paper 
or cloths so that the roots will be free from particles of soil, we 
see near the growing point of the roots that the surface is 
covered with numerous slender, delicate, thread- 
like bodies, the root hairs. Let us place a por- 
tion of a small root containing some of these 
root hairs in water on a glass slip, and prepare it 
for examination with the microscope. We see 
that each thread, or root hair, is a continuous 
tube, or in other words it is a single cell which 
has become very much elongated. The proto- 
plasmic membrane lines the wall, and strands of 
protoplasm extend across at irregular intervals, the 
interspaces being occupied by the cell-sap. 

We should now draw under the cover glass 
some of the five per cent salt solution. The 
protoplasmic membrane moves away from the cell 
wall at certain points, showing that plasmolysis is 
taking place, that is, the diffusion current is out- 
ward so that the cell-sap loses some of its water, 
and the pressure from the outside moves the 
membrane inward. We should not allow the salt 
solution to work on the root hairs long. It should 
be very soon removed by drawing in fresh water 
before the protoplasmic membrane has been 
broken at intervals, as is 
apt to be the case by the 
strong diffusion current 
and the consequent 
strong pressure f r o m 
without 
of protoplasm now moves 

outward as the diffusion current is inward, and soon regains its 
former position next the inner side of the cell wall. The 
root hairs then, like other parts of the plant which we have 









Fig. 27. 
Root hair of corn 
Fig. 26. before and after 

The membrane Seedling of radish, showing root treatment with 5^ 
hairs. salt solution. 



20 



PHYSTOLOGY. 



investigated, have the power of taking up water under press- 
ure. 

40. Cell-sap a solution of certain substances. — From these experiments we 
are led to believe that certain substances reside in the cell-sap of plants, which 
behave very much like the salt solution when separated from water by the 
protoplasmic membrane. Let us attempt to interpret these phenomena by 
recourse to diffusion experiments, where an animal membrane separates two 
liquids of different concentration. 

41. An artificial cell to illustrate turgor. — Fill a small wide-mouthed 
vial with a very strong sugar solution. Over the mouth tie firmly a piece 
of bladder membrane. Be certain that as the membrane is tied over the 
open end of the vial, the sugar solution fills it in order to keep out air- 




Fig. 28. Puncturing 
a make-believe cell 
after it has been 
lying in water. 




•^ 



Fig. 29. Same as Fig. 28 
after needle is removed. 



bu! .bles. Sink the vial in a vessel of fresh water and leave it there for twenty- 
four hours. Remove the vial and note that the membrane is arched out- 
vvard. Thrust a sharp needle through the membrane when it is arched 
outward, and quickly pull it out. The liquid spurts out because of the 
inside pressure. 

42. Diffusion through an animal membrane. — For this experiment we 
may use a thistle tube, across the larger end of which should be stretched and 
tied tightly a piece of a bladder membrane. A strong sugar solution (three 
parts sugar to one part water) is now placed in the tube so that the bulb is 



ABSORPTION, DIFFUSION, OSMOSE. 21 

filled and the liquid extends part way in the neck of the tube. This is im- 
mersed in water within a wide-mouth bottle, the neck of the tube being sup- 
ported in a perforated cork in such a way that the sugar solution in the tube is 
on a level with the water in the bottle or jar. In a short while the liquid 
begins to rise in the thistle tube, in the course of several hours having risen 
several centimeters. The diffusion current is thus stronger through the mem- 
brane in the direction of the sugar solution, so that this gains more water than 
it loses. 

We have here two liquids separated by an animal membrane, water on 
the one hand which diffuses readily through the membrane, while on the other 
is a solution of sugar which diffuses through the animal membrane with diffi- 
culty. The water, therefore, not containing any solvent, according to a 
general law which has been found to obtain in such cases, diffuses more 
readily through the membrane into the sugar solution, which thus increases in 
volume, and also becomes more dilute. The bladder membrane is what is 
sometimes called a diffusion membrane, since the diffusion currents travel 
through it. 

43. In this experiment then the bulk of the sugar solution is increased, and 
the liquid rises in the tube by this pressure above the level of the water in the 
jar outside of the thistle tube. The diffusion of liquids through a membrane 
is osmosis. 

44. Importance of these physical processes in plants. — Now if we recur 
to our experiment with spirogyra we find that exactly the same processes take 
place. The protoplasmic membrane is the diffusion membrane, through which 
the diffusion takes place. The salt solution which is first used to bathe the 
threads of the plant is a stronger solution than that of the cell -sap within the 
cell. Water therefore is drawn out of the cell-sap, but the substances in 
solution in the cell-sap do not readily move out. As the bulk of the cell- sap 
diminishes the pressure from the outside pushes the protoplasmic membrane 
away from the wall. Now when we remove the salt solution and bathe 
the thread with water again, the cell-sap, being a solution of certain sub- 
stances, diffuses with more difficulty than the water, and the diffusion current 
is inward, while the protoplasmic membrane moves out against the cell wall, 
and turgidity again results. Also in the experiments with salt and sugar solu- 
tions on the leaves of geranium, on the leaves and stems of the seedlings, on 
the tissues and cells of the beet and carrot, and on the root hairs of the seed- 
lings, the same processes take place. 

These experiments not only teach us that in the protoplasmic membrane, the 
cell wall, and the cell-sap of plants do we have structures which are capable of 
performing these physical processes, but they also show that these processes are 
of the utmost importance to the plant ; not only in giving the plant the power 
to take up solutions of nutriment from the soil, but they serve also other pur- 
poses, as we shall see later. 



CHAPTER III. 

HOW PLANTS OBTAIN WATER. 

In connection with the study of the means of absorption from the soil 
or water by plants, it will be found convenient to observe carefully the 
various forms of the plant. Without going into detail here, the suggestion 
is made that simple thread forms like spirogyra, cedogonium, and vau- 
cheria; expanded masses of cells as are found in the thalloid liverworts, 
the duckweed, etc., be compared with those liverworts, and with the mosses, 
where leaf -like expansions of a central axis have been differentiated. We 
should then note how this differentiation, from the physiological stand- 
point, has been carried farther in the higher land plants. 

45. Absorption by Algae and Fungi. — In the simpler forms of plant life, 
as in spirogyra and many of the algae and fungi, the plant body is not dif- 
ferentiated into parts.* In many other cases the only differentiation is 
between the growing part and the fruiting part. In the alga? and fungi 
there is no differentiation into stem and leaf, though there is an approach 
to it in some of the higher forms. Where this simple plant body is flat- 
tened, as in the sea-wrack, or ulva, it is a frond. The Latin word for 
frond is thallus, and this name is applied to the plant body of all the lower 
plants, the alga? and fungi. The algae and fungi together are sometimes 
called the thallophytes, or thallus plants. The word thallus is also some- 
times applied to the flattened body of the liverworts. In the foliose liver- 
worts and mosses there is an axis with leaf -like expansions. These are 
believed by some to represent true stems and leaves, by others to represent 
a flattened thallus in which the margins are deeply and regularly divided, or 
in which the expansion has only taken place at regular intervals. 

In nearly all of the algae the plant body is submerged in water. In these 



* See Chapter 38 for organization of members of the plant body. 

22 



HOW PLANTS OBTAIN WATER. 



23 



cases absorption takes place through all portions of the surface in contact 
with the water, as in spirogyra, vaucheria, and all of the larger seaweeds. 
Comparatively few of the algse grow on the surfaces of rocks or trees. In 
these examples it is likely that at times only portions of the plant body 
serve in the process of absorption of water from the substratum. A few of 
the algae are parasitic, living in the tissues of higher plants, where they are 
surrounded by the water or liquids within the host. Absorption takes 
place in the same way in many of the fungi. The aquatic fungi are im- 
mersed in water. In other forms, like mucor, a portion of the mycelium 
is within the substratum, and being bathed by the water or watery solu- 
tions absorbs the same, while the fruiting portion and the aerial mycelium 
obtain their water and food solutions from the mycelium in the substratum. 
In higher fungi, like the mushrooms, the mycelium within the ground or 
decaying wood absorbs the water necessary for the fruiting portion; while 
in the case of the parasitic fungi the mycelium lies in the water or liquid 
within the host. 

46. Absorption by liverworts. — In many of the plants termed liverworts 
the vegetative part of the plant is a thin, flattened, more or less elongated 
green body know as a thallus. 

Riccia. — One of these, belonging to the genus riccia, is shown in fig. 30. 
Its shape is somewhat like that 
of a minute ribbon which is 
forked at intervals in a dichot- 
omous manner, the character- 
istic kind of branching found in 
these thalloid liverworts. This 
riccia (known as R. lutescens) 
occurs on damp soil; long, 
slender, hair-like processes grow 
out from the under stirface of 
the thallus which resemble root 
hairs and serve the same pur- 
pose in the processes of absorp- 
tion. Another species of riccia 
(R. crystallina) is shown in fig. 
252. This plant is quite circular in outline and occurs on muddy flats. 
Some species float on the water. 




Fig. 30. 
Thallus of Riccia lutescens. 



47. Marchantia. — One of the larger and coarser liverworts is 
figured at 31. This is a very common liverwort, growing in 
very damp and muddy places and also along the margins of 
streams, on the mud or upon the surfaces of rocks which are 



24 PHYSIOLOGY. 

bathed with the water. This is known as Marchantia poly- 
morpha. If we examine the under surface of the marchantia 
we see numerous hair-like processes which attach the plant to 
the soil. Under the microscope we see that some of these are 
similar to the root hairs of the seedlings which we have been 
studying, and they serve the purpose of absorption. Since, how- 
ever, there are no roots on the marchantia plant, these hair-like 




Fig. si. 

Marchantia plant with cupules and gemmae; rhizoids below. 



outgrowths are usually termed here rhizoids. In marchantia they 
are of two kinds, one kind the simple ones with smooth walls, 
and the other kind in which the inner surfaces of the walls are 
roughened by processes which extend inward in the form of irreg- 
ular tooth-like points. Besides the hairs on the under side of 
the thallus we note especially near the growing end that there are 
two rows of leaf -like scales, those at the end of the thallus curv- 
ing up over the growing end, thus serving to protect the delicate 
tissues at the growing point, 



HOW PLANTS OBTAIN WATER. 



25 



48. Frullania. — In fig. 32 is shown another liverwort, which 
differs greatly in form from the ones we have 
just been studying in that there is a well-defined 
axis with lateral leaf-like outgrowths. Such liver- 
worts are called foliose liverworts. Besides these 
two quite prominent rows of leaves there is a 
third row of poorly developed leaves on the under 

surface. Also 
from the 
under surface 
of the axis 
we see here 
and there 
slender out- 
the 






Fig. 32. 

Portion of plant of 
Frullania, a foliose 

liverwort. 



Fig. 33- 
Portion of same 
more highly magni- 
fied, showing over- 
lapping leaves. 



Fig. 34. growths, 

Under side, 
showing forked rhlZOlQS, 
under row of 

leaves and lobes t ll r O U g h 
of lateral leaves. ... 

which much 



of the water is absorbed. 

49. Absorption by the mosses. 



Among the mosses, which are 
^s usually common in moist and shaded 
situations, examples are abundant 
which are suitable for the study of 
the organs of absorption. If we take 
for example a plant of mnium 
(M. affine), which is illustrated in fig. 
36, we note that it consists of a slender 





Fig. 3 5- 
Foliose liverwort (bazzania) showing dichotomous branching and overlapping leaves. 

axis with thin flat, green, leaf -like expansions, Examining with 



26 



PHYS10L0G Y. 



the microscope the lower end of the axis, which is attached to 

the substratum, there are seen numerous brown-colored threads 

more or less branched. 

50. Absorption by the higher aquatic plants. — Examples of 

the water plants which are entirely submerged in water are the 
water-crowfoots, some of the pond- 
weeds, elodea or water-weeds, the tape- 
grass, vallisneria, etc. In these plants 
all parts of the body being submerged, 
they absorb water with which they are 
in contact. In other aquatic plants, like 
the water-lilies, some of the pond- 
weeds, the duck-meats, etc., are only 
partially submerged in the water; the 
upper surface of the leaf or of the leaf- 
like expansion being exposed to the air, 
while the under surface lies in close 
contact with the water, and the stems 
and the petioles of the leaves are also 
immersed in water. In these plants 
absorption takes place through those 
parts in contact with the water. 

51. Absorption by the duck-meats. 
— These plants are very curious ex- 
amples of the higher plants. 

Lemna. — One of these is illustrated in fig. 

37. This is the common duckweed, Lemna 

trisidca. It is very peculiar in form and in 

its mode of growth. Each one of the lateral 

leaf-like expansions extends outwards by the 

Fig- 36. elongation of the basal part, which becomes 

Female plant (gametophvte) , j 1 j > T 1 ^ 1 

of a moss (milium), showing lon g and slender. Next, two new lateral ex- 

rhizoids below and the tuft of pa nsions are formed on these by prolification 
leaves above, which protect the r J r 

archegonia. from near the base, and thus the plant con- 

tinues to extend. The plant occurs in ponds and ditches and is sometimes 
very common and abundant. It floats on the surface of the water. While 
the flattened part of the plant resembles a leaf, it is really the stem, no 
leaves being present. This expanded green body is usually termed a 




HOW PLANTS OB 7 'A IN WATER. 27 

"frond." A single rootlet grows out from the under side and is destitute 




Fig. 3 7- 
Fronds of the duckweed (Lemna trisculca). 

of root hairs. Absorption of water therefore takes place through this rootlet 
and through the under 
side of the "frond." 

52. Spirodela poly- 
rhiza. — This is a very 
curious plant, closely re- 
lated to the lemna and 
sometimes placed in the 
same genus. It occurs 
in similar situations, and pj g 3 g 
is very readily grown in Spirodela polyrhiza. 
aquaria. It reminds one of a little insect as 
seen in fig. 38. There are several rootlets on 
the under side of the frond. Absorption of 
water takes place here in the same way as in 
lemna. 

53. Absorption in wolffia. — Perhaps the most curious of these modified 
water plants is the little wolffia, which contains the smallest specimens of 
the flowering plants. Two species of this genus are shown in figs. 39-41. 
The plant body is reduced to nothing but a rounded or oval green body, 
which represents the stem. No leaves or roots are present. The plants 
multiply by "prolification," the new fronds growing out from a depression 
on the under side of one end. Absorption takes place through the under 
surface. 

54. Absorption by land plants. — Water cultures. — In connec- 
tion with our inquiry as to how land plants obtain their water, it 




28 



PHYSIOLOGY. 



will be convenient to prepare some water cultures to illustrate 
this and which can also be used later in our study of nutrition 
(Chapter IX). 




Fig. 39- Fig. 40. Fig. 41. 

Young frond of wo] ffia Young frond of wolffia Another species of 

growing out of older one. separating trom older one. wolffia . the two fronds 

still connected. 

Chemical analysis shows that certain mineral substances are 
common constituents of plants. By growing plants in different 
solutions of these various substances it has been possible to deter- 
mine what ones are necessary constituents of plant food. While 
the proportion of the mineral elements which enter into the com- 
position of plant food may vary considerably within certain 
limits, the concentration of the solutions should not exceed cer- 
tain limits. A very useful solution is one recommended by Sachs, 
and is as follows: 

55. Formula for water cultures : 

Water 1000 cc. 

Potassium nitrate o . 5 gr. 

Sodium chloride o . 5 " 

Calcium sulphate o . 5 ' ' 

Magnesium sulphate. o . 5 ' ' 

Calcium phosphate o . 5 ' ' 

The calcium phosphate is only partly soluble. The solution which is not in 
use should be kept in a dark cool place to prevent the growth of minute algae. 

56. Several different plants are useful for experiments in water cultures, 
as peas, corn, beans, buckwheat, etc. The seeds of these plants may be 
germinated, after soaking them for several hours in warm water, by placing 



HOW PLANTS OBTAIN WAT&R. 



29 



them between the folds of wet paper on shallow trays, or in the folds of wet 
cloth. The seeds should not be kept immersed in water after they have 
imbibed enough to thoroughly soak and swell them. At the same time 
that the seeds are placed in damp paper or cloth for germination, one lot of 
the soaked seeds should be planted in good soil and kept under the same 
temperature conditions, for control. When the plants have germinated 
one series should be grown in distilled water, which possesses no plant food; 
another in the nutrient solution, and still another in the nutrient solution to 
which has been added a few drops of a solution of iron chloride or ferrous 
sulphate. There would then be four series of cultures which should be 
carried out with the same kind of seed in each series so that the compari- 
sons can be made on the same species under the different conditions. The 
series should be numbered and recorded as follows: 

No. I, soil. 

No. 2, distilled water. 

No. 3, nutrient solution. 

No. 4, nutrient solution with a few drops of iron solution added. 

57. Small jars or wide-mouth bottles, or crockery jars, can be used for the 
water cultures, and the cultures are set up as follows : A cork which will just 
fit in the mouth of the bottle, or which can be supported by pins, is perforated 
so that there is room to insert the seedling, 
with the root projecting below into the liquid. 
The seed can be fastened in position by insert- 
ing a pin through one side, if it is a large one, 
or in the case of small seeds a cloth of a coarse 
mesh can be tied over the mouth of the bottle 
instead of using the cork. After properly set- 
ting up the experiments the cultures should be 
arranged in a suitable place, and observed from 
time to time during several weeks. In order to 
obtain more satisfactory results several dupli- 
cate series should be set up to guard against the 
error which might arise from variation in indi- 
vidual plants and from accident. Where there 
are several students in a class, a single series 
set up by several will act as checks upon one 
another. If glass jars are used for the liquid 
cultures they should be wrapped with black 
paper or cloth to exclude the light from the 
liquid, otherwise numerous minute algre are apt to grow and interfere with the 
experiment. Or the jars may be sunk in pots of earth to serve the same 
purpose. If crockery jars are used they will not need covering. 

58. For some time all the plants grow equally well, until the nutriment 
Stored in the seed is exhausted. The numbers 1, 3 and 4, in soil and nutri* 




Fig. 42. 

Culture cylinder to show position of 

corn seedling (Hansen). 



30 



PHYSIOLOGY. 



ent solutions, should outstrip number 2, the plants in the distilled water. 
No. 4 in the nutrient solution with iron, having a perfect food, compares favor- 
ably with the plants in the soil. 

59. Plants take liquid food from the soil. — From these ex- 
periments then we judge that such plants take up the food they 
receive from the soil in the form of a liquid, the elements being 
in solution in water. 

If we recur now to the experiments which were performed with 
the salt solution in producing plasmolysis in the cells of spirogyra, 
in the cells of the beet or corn, and in the root hairs of the corn 
and bean seedlings, and the way in which these cells become tur- 
gid again when the salt solution is removed and they are again 
bathed with water, we shall have an explanation of the way in 
which plants take up nutrient solutions of food material through 
their roots. 

60. How food solutions are carried into the plant. — We can 




Fig. 4.3. 
Section of corn root, showing rhiz^iJ.3 formed from elongated epidermal cells. 

see how water and food solutions are carried into the plant, 



HO W PLANTS OBTAIN WATER. 3 1 

and we must next turn our attention to the way in which these 
solutions are carried farther into the plant. We should make a 
section across the root of a seedling in the region of the root 
hairs and examine it with the aid of a microscope. We here see 
that the root hairs are formed by the elongation of certain of the 
surface cells of the root. These cells elongate perpendicularly to 
the root, and become $mm to 6mm long. They are flexuous or 
irregular in outline and cylindrical, as shown in fig. 43. The 
end of the hair next the root fits in between the adjacent superfi- 
cial cells of the root and joins closely to the next deeper layer of 
cells. In studying the section of the young root we see that the 
root is made up of cells which lie closely side by side, each with 
its wall, its protoplasm and cell-sap, the protoplasmic membrane 
lying on the inside of each cell wall. 

61. In the absorption of the watery solutions of plant food by the root 
hairs, the cell-sap, being a more concentrated solution, gains some of the 
former, since the liquid of less concentration flows through the protoplasmic 
membrane into the more concentrated cell-sap, increasing the bulk of the lat- 
ter. This makes the root hairs turgid, and at the same time dilutes the cell- 
sap so that the concentration is not so great. The cells of the root lying in- 
side and close to the base of the root hairs have a cell-sap which is now more 
concentrated than the diluted cell-sap of the hairs, and consequently gain 
some of the food solutions from the latter, which tends to lessen the content 
of the root hairs and also to increase the concentration of the cell-sap of the 
same. This makes it possible for the root hairs to draw on the soil for more 
of the food solutions, and thus, by a variation in the concentration of the sub- 
stances in solution in the cell-sap of the different cells, the food solutions are 
carried along until they reach the vascular bundles, through which the solu- 
tions are carried to distant parts of the plant. Some believe that there is a 
rhythmic action of the elastic cell walls in these cells between the root hairs and 
the vascular bundles. This occurs in such a way that, after the cell becomes 
turgid, it contracts, thus reducing the size of the cell and forcing some of the 
food solutions into the adjacent cells, when by absorption of more food solu- 
tions, or water, the cell increases in turgidity again. This rhythmic action of 
the cells, if it does take place, would act as a pump to force the solutions 
along, and would form one of the causes of root pressure. 

62. How the root hairs get the watery solutions from the soil. — If we 
examine the root hairs of a number of seedlings which are growing in the soil 
under normal conditions, we shall see that a large quantity of soil readily 
clings to the roots. We should note also that unless the soil has been recently 
watered there is no free water in it ; the soil is only moist. We are curious 



V 



PHYSIOLOGY. 



to know how plants can obtain water from soil which is not wet. If we at* 
tempt to wash off the soil from the roots, being careful not to break away the 




Fig. 44- 
Root hairs of corn seedling with soil particles adhering closely. 

roo: hairs, we find that small particles cling so tenaciously to 
the root hairs that they are not removed. Placing a few such 
root hairs under the microscope it appears as if here and there the root hairs 
were glued to the minute soil particles. 

CO. If now we take some of the soil which is only moist, weigh it, and 
then permit it to become quite dry on exposure to dry air, and weigh again, 
we find that it loses weight in drying. Moisture has been given oft. 
This moisture, it has been found, forms an exceedingly thin film on the sur- 
face of the minute soil particles. Where these soil particles lie closely to- 
gether, as they usually do when massed together in the pot or elsewhere, this 
thin film of moisture is continuous from the surface of one particle to that of an- 
ther. Thus the soil particles which are so closely attached to the root hairs 
connect the surface of the root hairs with this film of moisture. As the cell- 
sap of the root hairs draws on the moisture film with which they are in con- 
tact, the tension of this film is sufficient to draw moisture from distant partis 
cles. Tn this way the roots are supplied with water in soil which is only 
moist. 

64. Plants cannot remove all the moisture from the soil. — If we now take 
a potted plant, or a pot containing a number of seedlings, place it in a moder- 
ately dry room, and do not add water to the soil we find in a few days that 
the plant is wilting. The soil if examined will appear quite dry to the 
sense of touch. Let us weigh some of this soil, then dry it by artificial 



HOW PLANTS OBTAIN WATER. 33 

heat, and weigh again. It has lost in weight. This has been brought about 
by driving off the moisture which still remained in the soil after the plant 
began to wilt. This teaches that while plants can obtain water from soil 
which is only moist or which is even rather dry, they are not able to with- 
draw all the moisture from the soil. 

65. " Root pressure " or exudation pressure. — It is a very com- 
mon thing to note, when certain shrubs or vines are pruned in 
the spring, the exudation of a watery fluid from the cut surfaces. 
In the case of the grape vine this has been known to continue for 
a number of days, and in some cases the amount of liquid, called 
"sap," which escapes is considerable. In many cases it is 
directly traceable to the activity of the roots, or root hairs, in 
the absorption of water from the soil. For this reason the term 
root pressure has been used to denote the force exerted in sup- 
plying the water from the soil. But there are some who object 
to the use of this term "root pressure." The principal objec- 
tion is that the pressure which brings about the phenomenon 
known as ' ' bleeding ' ' by plants is not present in the roots alone. 
This pressure exists under certain conditions in all parts of the 
plant. The term exudation pressure has been proposed in lieu 
of root pressure. It should be remembered that the movement 
of water in the plant is started by the pressure which exists in 
the root. If the term "root pressure" is used, it should be 
borne clearly in mind that it does not express the phenomenon 
exactly in all cases. 

Root pressure may be measured. — It is possible to measure 
not only the amount of water which the roots will raise in a 
given time, but also to measure the force exerted by the roots 
during root pressure. It has been found that root pressure in 
the case of the nettle is sufficient to hold a column of water about 
4.5 meters (15 ft.) high (Vines), while the root pressure of the 
vine (Hales, 1721) will hold a column of water about 10 meters 
(36.5 ft.) high, and the birch (Betula lutea) (Clark, 1873) has a 
root pressure sufficient to hold a column of water about 25 meters 
(84.7 ft.) high. 

66. Experiment to demonstrate root pressure. — By a very simple method 
this lifting of water by root pressure is shown. During the summer season 



34 



PHYSlOLOG V. 



plants in the open may be used if it is preferred, but pJants grown in pots 
are also very serviceable, and one may use a potted begonia or balsam, the 
latter being especially useful. The plants are usually convenient to obtain 
from the greenhouses, to illustrate this phenomenon. 
The stem is cut off rather close to the soil and a long 
glass tube is attached to the cut end of the stem, still 
connected with the roots, by the use of rubber tubing, 
as shown in figure 45, and a very small quantity of water 
may be poured in to moisten the cut end of the stem. 
In a few minutes the water begins to rise in the glass 
tube. In some cases it rises quite rapidly, so that the 
column of water can readily be seen to extend higher 
and higher up in the tube when observed at quite 
short intervals. (To measure the force of root pressure 
is rather difficult for elementary work. To measure it 
see Ganong, Plant Physiology, pp. 67, 68, or some other 
book for advanced work.) 

67. In either case where the experiment is 
continued for several days it is noticed that the 
column of water or of mercury rises and falls at 
different times during the same day, that is, the 
column stands at varying heights; or in other 
words the root presssure varies during the day. With some plants 
it has been found that the pressure is greatest at certain times 
of the day, or at certain seasons of the year. Such variation 
of root pressure exhibits what is termed a periodicity, and in 
the case of some plants there is a daily periodicity; while in 
others there is in addition an annual periodicity. With the 
grape vine the root pressure is greatest in the forenoon, and 
decreases from 12-6 p.m., while with the sunflower it is greatest 
before 10 a.m., when it begins to decrease. Temperature of 
the soil is one of the most important external conditions affect- 
ing the activity of root pressure. 



Fig. 45. 

Experiment to 
show root pressure 
(Detmer). 



CHAPTER IV. 

TRANSPIRATION, OR THE LOSS OF WATER BY 
PLANTS. 

68. We should now inquire if all the water which is taken up 
in excess of that which actually suffices for turgidity is used in the 
elaboration of new materials of construction. We notice when a 
leaf or shoot is cut away from a plant, unless it is kept in quite 
a moist condition, or in a damp, cool place, that it becomes flac- 
cid, and droops. It wilts, as we say. The leaves and shoot lose 
their turgidity. This fact suggests that there has been a loss of 
water from the shoot or leaf. It can be readily seen that this 
loss is not in the form of drops of water which issue from the cut 
end of the shoot or petiole. Whajt then becomes of the water in 
the cut leaf or shoot ? 




Fig. 46. 
To show loss of water from leaves, the leaves just covered. 

69. Loss of water from excised leaves. — Let us take a handful 
of fresh, green, rather succulent leaves, which are free from 

35 



3$ 



PHYSIOLOGY. 



water on the surface, and place them under a glass bell jar, which 
is tightly closed below but which contains no water. Now place 
this in a brightly lighted window, or in sunlight. In the course 
of fifteen to thirty minutes we notice that a thin film of moisture 
is accumulating on the inner surface of the glass jar. After an 
hour or more the moisture has accumulated so that it appears in 
the form of small drops of condensed water. We should set up 
at the same time a bell jar in exactly the same way but which 
contains no leaves. In this jar there is no condensed moisture 
on the inner surface. We thus are justified in concluding that 




Fig. 47- 
After a few hours drops of water have accumulated on the inside of the jar covering 

the leaves. 



the moisture in the former jar comes from the leaves. Since 
there is no visible water on the surfaces of the leaves, or at the 
cut ends, before it may have condensed there, we infer that the 
water escapes from the leaves in the form of water vapor, and 
that this water vapor, when it comes in contact with the surface 
of the cold glass, condenses and forms the moisture film, and 
later the drops of water. The leaves of these cut shoots there- 
fore lose water in the form of water vapor, and thus a loss of 
turgidity results. 

70. Loss of water from growing plants. — Suppose we now 
take a small and actively growing plant in a pot, and cover the 
pot and the soil with a sheet of rubber cloth or flexible oilcloth 



TRANSPIRATION. 37 

which fits tightly around the stem of the plant so that the mois- 
ture from the soil or from the surface of the pot cannot escape. 
Then place a bell jar over the plant, and set in a brightly lighted 
place, at a temperature suitable for growth. In the course of a 
few minutes on a dry day a moisture film forms on the inner 
surface of the glass, just as it did in the case of the glass jar con- 
taining the cut shoots and leaves. Later the moisture has con- 
densed so that it is in the form of drops. If we have the same 
leaf surface here as we had with the cut shoots, we shall prob- 
ably find that a larger amount of water accumulates on the 
surface of the jar from the plant that is still attached to its 
roots. 

71. Water escapes from the surfaces of living leaves in the 
form of water vapor. — This living plant then has lost water, which 
also escapes in the form of water vapor. Since here there are no 
cut places on the shoots or leaves, we infer that the loss of water 
vapor takes place from the surfaces of the leaves and from the 
shoots. It is also to be noted that, while this plant is losing 
water from the surfaces of the leaves, it does not wilt or lose its 
turgidity. The roots by their activity and pressure supply water 
to take the place of that which is given off in the form of water 
vapor. This loss of water in the form of water vapor by plants 
is transpiration. 

72. A test for the escape of water vapor from plants. — Make 
a solution of cobalt chloride in water. Saturate several pieces of 
filter paper with it. Allow them to dry. The water solution of 
cobalt chloride is red. The paper is also red when it is moist, 
but when it is thoroughly dry it is blue. It is very sensitive 
to moisture and the moisture of the air is often sufficient to 
redden it. Before using dry the paper in an oven or over a 
flame. 

73. Take two bell jars, as shown in fig. 49. Under one place 
a potted plant, the pot and earth being covered by oiled paper. 
Or cover the plant with a fruit jar. To a stake in the pot pin a 
piece of the dried cobalt paper, and at the same time pin to a 



38 



PHYSIOLOG y. 



stake, in another jar covering no plant, another piece of cobalt 
paper. They should both be put under the jars at the same 
time. In a few moments the paper in the jar with the plant will 
begin to redden. In a short while, ten or fifteen minutes, prob- 
ably, it will be entirely red, while the paper under the other jar 
will remain blue, or be only slightly reddened. The water vapor 
passing off from the living plant comes in contact with the sensi- 




Fig. 48. Fig. 49- 

Fig. 48. — Water vapor is given off by the leaves when attached to the living plant. 
It condenses into drops of water on the cool surface of the glass covering the plant. 

Fig. 49. — A good way to show that the water passes off from the leaves in the form 
of water vapor. 



tive cobalt chloride in the paper and reddens it before there is 
sufficient vapor present to condense as a film of moisture on the 
surface of the jar. 

74. Experiment to compare loss of water in a dry and a 
humid atmosphere. — We should now compare the escape of 
water from the leaves of a plant covered by a bell jar, as in the 
last experiment, with that which takes place when the plant is 



TRANSPIRA TIOAT. 39 

exposed in a normal way in the air of the room or in the open. 
To do this we should select two plants of the same kind growing 
in pots, and of approximately the same leaf surface. The potted 
plants are placed one each on the arms of a scale. One of the 
plants is covered in this position with a bell jar. With weights 
placed on the pan of the other arm the two sides are balanced. 
In the course of an hour, if the air of the room is dry, moisture 
has probably accumulated on the inner surface of the glass jar 
which is used to cover one of the plants. This indicates that 
there has here been a loss of water. But there is no escape of 
water vapor into the surrounding air so that the weight on this 
arm is practically the same as at the beginning of the experiment. 
We see, however, that the other arm of the balance has risen. 
We infer that this is the result of the loss of water vapor from the 
plant on that arm. Now let us remove the bell jar from the other 
plant, and with a cloth wipe off all the moisture from the inner 
surface, and replace the jar over the plant. We note that the 
end of the scale which holds this plant is still lower than the 
other end. 

75. The loss of water is greater in a dry than in a humid 
atmosphere. — This teaches us that while water vapor escaped 
from the plant under the bell jar. the air in this receiver soon 
became saturated with the moisture, and thus the farther escape 
of moisture from the leaves was checked. It also teaches us an- 
other very important fact, viz. , that plants lose water more rapidly 
through their leaves in a dry air than in a humid or moist atmos- 
phere. We can now understand why it is that during the very 
hot and dry part of certain days plants often wilt, while at night- 
fall, when the atmosphere is more humid, they revive. They lose 
more water through their leaves during the dry part of the day, 
other things being equal, than at other times. 

76. How transpiration takes place. — Since the water of 
transpiration passes off in the form of water vapor we are led to 
inquire if this process is simply evaporation of water through the 
surface of the leaves, or whether it is controlled to any appreci- 
able extent by any condition of the living plant. An experiment 



40 ¥ PH YSIOL OGY. 

which is instructive in this respect we shall find in a comparison 
between the transpiration of water from the leaves of a cut shoot, 
allowed to lie unprotected in a dry room, and a similar cut shoot 
the leaves of which have been killed. 

77. Almost any plant will answer for the experiment. For this purpose I 
have used the following method. Small branches of the locust (Robinia 
pseudacacia), of sweet clover (Melilotus alba), and of a heliopsis were 
selected. One set of the shoots was immersed for a moment in hot water near 
the boiling point to kill them. The other set was immersed for the same 
length of time in cold water, so that the surfaces of the leaves might be well 
wetted, and thus the two sets^ of leaves at the beginning of the experiment 
would be similar, so far as the amount of water on their surfaces is con- 
cerned. All the shoots were then spread out on a table in a dry room, the 
leaves of the killed shoots being separated where they are inclined to cling 
together. In a short while all the water has evaporated from the surface of 
the living leaves, while the leaves of the dead shoots are still wet on the sur- 
face. In six hours the leaves of the dead shoots from which the surface 
water had now evaporated were beginning to dry up, while the leaves of the 
living plants were only becoming flaccid. In twenty -four hours the leaves 
of the dead shoots were crisp and brittle, while those of the living shoots were 
only wilted. In twenty-four hours more the leaves of the sweet clover and 
of the heliopsis were still soft and flexible, showing that they still contained 
more water than the killed shoots which had been crisp for more than a 
day. 

78. It must be then that during what is termed transpiration the living 
plant is capable of holding back the water to some extent, which, in a dead 
plant would escape more rapidly by evaporation. It is also known that a 
body of water with a surface equal to that oi z. given leaf surface of a plant 
loses more water by evaporation during the same length of time than the 
plant loses by transpiration. 

79. Structure of a leaf. — We are now led to inquire why it is 
that a living leaf loses water less rapidly than dead ones, and 
why less water escapes from a given leaf surface than from an 
equal surface of water. To understand this it will be necessary 
to examine the minute structure of a leaf. For this purpose \vr 
may select the leaf of an ivy, though many other leaves will 
answer equally well. From a portion of the leaf we should make 
very thin cross sections with a razor or other sharp instrument. 
These sections should be perpendicular to the surface of the leaf 



TRANSPIRA TION. 



41 




Fig. 50. 
Section through ivy leaf showing 



and should be then mounted in water for microscopic examina- 
tion.* 

80. Epidermis of the leaf. — In this section we see that the 
green part of the leaf is bordered on what are its upper and 
lower surfaces by a row of cells which 
possess no green color. The walls of 
the cells of each row have nearly par- 
allel sides, and the cross walls are per- 
pendicular. These cells form a single 
layer over both surfaces of the leaf and 
are termed the epidermis. Their walls 
are quite stout and the outer walls are 
cuiicularized. 

81. Soft tissue of the leaf. — The 
cells which contain the green chloro- 
phyll bodies are arranged in two dif- 
ferent Ways. Those OII the Upper Sl'de communication between stomateanc 

J >■ x the large intercellular spaces ot the 

of the leaf are usually long and pris- leaf ' stoma closed, 
matic in form and lie closely parallel to each other. Because of 
this arrangement of these cells they are termed the palisade cells, 
and form what is called the palisade layer. The other green 

cells, lying below, 
vary greatly in size in 
different plants and to 
some extent also in the 
same plant. Here we 
notice that they arc 
elongated, or oval, or 
somewhat irregular in 
form. The most striking peculiarity, however, in their arrange- 
ment is that they are not usually packed closely together, but each 
cell touches the other adjacent cells only at certain points. This 
arrangement of these cells forms quite large spaces between them, 
the intercellular spaces. If we should examine such a section of 
a leaf before it is mounted in water we would see that the inter- 
* Demonstrations may be made with prepared sections of leaves, 




Fig. 51. 

Stoma open. 

Figs. 34, 35.— Section through stomata of ivy leaf. 



42 



PHYSIOLOG Y. 



cellular spaces are not filled with water or cell-sap, but are filled 
with air or some gas. Within the cells, on the other hand, we 
find the cell-sap and the protoplasm. 

82. Stomata. — If we examine carefully the row of epidermal 
cells on the under surface of the leaf, we find here and there 
a peculiar arrangement of cells shown at figs. 51, 52. This 

opening 
through the 
epi dermal 
layer is a 
stoma. The 
cells which 
i m mediately 
surround the 




Fig. 53. 
Portion of epidermis of ivy, showing irregular epiderma 
and guard cells. 



cells 



openings are 

the guard 

stoma cells. T h e 

form of the 

guard cells can be better seen if we tear a leaf in such a way as 
to strip off a short piece of the lower epidermis, and mount this 
in water. The guard cells are nearly crescent shaped, and the 
stoma is elliptical in outline. The epidermal cells are very 
irregular in outline in this view. We should also note that while 
the epidermal cells contain no chlorophyll, the guard cells do. 

82a. In the ivy leaf the guard cells are quite plain, but in most 
plants the form as seen in cross-section is irregular in outline, as 
shown in fig. 530, which is from a section of a wintergreen leaf. 
This leaf is interesting because it shows the characteristic struc- 
ture of leaves of many plants growing in soil where absorption of 
water by the roots is difficult owing to the cold water, acids, or 
salts in the water or soil, or in dry soil (see Chapters 47, 54? 55)* 
The cuticle over the upper epidermis is quite thick. This 
lessens the loss of water by the leaf. The compact palisades of 
cells are in two to three cell layers, also reducing the loss of water. 

83. The living protoplasm retards the evaporation of water from the 
leaf, — If we now take into consideration a few facts which we have learned 



TRANSPIRA TION. 



43 



in a previous chapter, with reference to the physical properties of the living 
cell, we shall be able to give a partial explanation of the comparative slow- 
ness with which the water escapes from the leaves. The inner surfaces of 
the cell walls are lined with the membrane of protoplasm, and within this 
is the cell-sap. These cells have become turgid by the absorption of the 




Fig. 53a. 
Cross-section of leaf of wintergreen. Cu. cuticle; Epid., epidermis; v.d., vascular 
duct; Int. c. sp., intercellular space; L. ep., lower epidermis; St., stoma. 



water which has passed up to them from the roots. While the protoplas- 
mic membrane of the cells does not readily permit the water to filter through, 
yet it is saturated with water, and the elastic cell wall with which it is in 
contact is also saturated. From the cell wall the water evaporates into the 
intercellular spaces. But the water is given up slowly through the proto- 
plasmic membrane, so that the water vapor cannot be given off as rapidly 
from the cell walls as it could if the protoplasm were dead. The living 
protoplasmic membrane then which is only slowly permeable to the water of 
the cell-sap is here a very important factor in checking the too rapid loss of 
water from the leaves. 



44 PHYSIO LOG V. 

By an examination of our leaf section we see that the intercellulai spaces 
are all connected, and that the stomata, where they occur, open also into 
intercellular spaces. There is here an opportunity for the water vapoi 
in the intercellular spaces to escape when the stomata are open, 

84. Action of the stomata. — The guard cells serve an important func- 
tion in regulating transpiration. During normal transpiration the guard 
cells are turgid and their peculiar form then causes them to arch away 
from each other, allowing the escape of water vapor. When the air becomes 
too dry transpiration is in excess of absorption by the roots. The guard 
cells lose some of their water, and collapse so that their inner faces meet 
in a straight line and close the stoma. Thus the rapid transpiration is 
checked. Some evaporation of water vapor, however, takes place through 
the epidermal cells, and if the air remains too dry, the leaves eventually 
become flaccid and droop. During the day the effect of sunlight is to 
increase certain sugars or salts in the guard cells so that they readily be- 
come turgid and open the stomates, but at night the cell-sap is less con- 
centrated and the stomates are usually closed. Light therefore favors 
transpiration, while in darkness transpiration is checked. 

85. Compare transpiration from the two surfaces of the leaf. — This can 
be done by using the cobalt chloride paper. This paper can be kept from 
year to year and used repeatedly. It is thus a very simple matter to make 
these experiments. Provide two pieces of glass (discarded glass nega- 
tives, cleaned, are excellent), two pieces of cobalt chloride paper, and some 
geranium leaves entirely free from surface water. Dry the paper until it is 
blue. Place one piece of the paper on a glass plate; place the geranium 
leaf with the under side on the paper. On the upper side of the leaf now 
place the other cobalt paper, and next the second piece of glass. On the 
pile place a light weight to keep the parts well in contact. In fifteen or 
twenty minutes open and examine. The paper next the under side of the 
geranium leaf is red where it lies under the leaf. The paper on the upper 
side is only slightly reddened. The greater loss of water, then, is through 
the under side of the geranium leaf. This is true of a great many leaves, 
but it is not true of all. 

86. Negative pressure. — This is not only indicated by the drooping of 
the leaves, but may be determined in another way. If the shoot of such a 
plant be cut underneath mercury, or underneath a strong solution of eosin, 
it will be found that some of the mercury or eosin, as the case may be, will 
be forcibly drawn up into the stem toward the roots. This is seen on 
quickly splitting the cut end of the stem. When plants in the open cannot 
be obtained in this condition, one may take a plant like a balsam plant 
from the greenhouse, or some other potted plant, knock it out of the pot, 
free the roots from the soil and allow to partly wilt. The stem may then 
be held under the eosin solution and cut. 



TRANSP1RA TIO AT. 



45 




Fig. 54- 
Experiment to 
show lifting power of 
transpiration. 



87. Lifting power of transpiration. — Not only does transpiration go on 
quite independently of root pressure, as we have discovered from other 
experiments, but transpiration is capable of exerting a 
lifting power on the water in the plant. This may 
be demonstrated in the following way: Place the cut 
end of a leafy shoot in one end of a U tube and fit it 
water-tight. Partly fill this arm of the U tube with 
water, and add mercury to the other arm until it 
stands at a level in the two arms as in fig. 54. In a 
short time we note that the mercury is rising in the 
tube. 

88. Root pressure may exceed transpiration. — If we 
cover small actively growing plants, such as the pea, 
corn, wheat, bean, etc., with a bell jar, and place them 
in the sunlight where the temperature is suitable for 
growth, in a few hours, if conditions are favorable, 
we shall see that there are drops of water standing out 
on the margins of the leaves. These drops of water 
have exuded through the ordinary stomata, or in 
other cases what are called water stomata, through 
the influence of root pressure. The plant being covered by the glass jar, 
the air soon becomes saturated with moisture and transpiration is checked. 
Root pressure still goes on, however, and the result is shown in the exuding 

drops. Root pressure is here in excess of transpiration. 
This phenomenon is often to be observed during the sum- 
mer season in the case of low-growing plants. During the 
bright warm day transpiration 

1 " ■"" ^"^ equals, or may be in excess of, 

Fig. S5 . root pressure, and the leaves 

Estimation of the amount of are consequently flaccid. As 
transpiration. The tubes are • , .r n .1 

filled with water, and as the m ghtfall comes on the air 
water transpires from the leaf becomes more moist, and the 
surface its movement in the tube 

from a to b can be measured, conditions of light are such 
(After Mangin.) , , . . . , 

also that transpiration is les- 
sened. Root pressure, however, is still active because the soil is still warm. 
In these cases drops of water may be seen exuding from the margins of the 
leaves due to the excess of root pressure over transpiration. Were it not 
for this provision for the escape of the excess of water raised by root pres- 
sure, serious injury by lesions, as a result of the great pressure, might 
result. The plant is thus to some extent a self-regulatory piece of 
apparatus so far as root pressure and transpiration are concerned. 

89. Injuries caused by excessive root pressure.— Some varieties of toma- 
toes when grown in poorly lighted and poorly ventilated greenhouses suffer 




46 



PHYSIOLOGY. 



serious injury through lesions of the tissues. This is brought about by the 
cells at certain parts becoming charged so full with water through the 
activity of root pressure and lessened transpiration, assisted also probably 
by an accumulation of certain acids in the cell-sap which cannot be got 
rid of by transpiration. Under these conditions some of the cells here 
swell out, forming extensive cushions, and the cell walls become so weak- 
ened that they burst. It is possible to imitate the excess of root pressure 
in the case of some plants by connecting the stems with a system of 

water pressure, when very quickly 
the drops of water will begin to 
exude from the margins of the 
leaves. 

90. It should be stated that in 
reality there is no difference between 
transpiration and evaporation, if we 
bear in mind that evaporation takes 
place more slowly from living plants 
than from dead ones, or from an 
equal surface of water. 

91. The escape of water vapor is 
not the only function of the stomata. 
The exchange of gases takes place 
through them as we shall later see. 
A large number of experiments show 
that normally the stomata are open 
when the leaves are turgid. But 
when plants lose excessive quantities 
of water on dry and hot days, so 
that the leaves become flaccid, the 
guard cells automatically close the 
stomata to check the escape of water 
vapor. Some water escapes through 
the epidermis of many plants, 
though the cuticularized mem- 
brane of the epidermis largely prevents evaporation. In arid regions 
plants are usually provided with an epidermis of several layers of cells to 
more securely prevent evaporation there. In such cases the guard cells 
are often protected by being sunk deeply in the epidermal layer. 

92. Demonstration of stomates and intercellular air spaces. — A good 
demonstration of the presence of stomates in leaves, as well as the presence 
and intercommunication of the intercellular spaces, can be made by blow- 
ing into the cut end of the petiole of the leaf of a calla lily, the lamina being 




Fig. 56. 

The roots are lifting more water into 

the plant than can be given off in the form 

of water vapor, so it is pressed out in 

drops. From " First Studies Plant Life." 



TRANSPIRA notf. 47 

immersed in water. The air is forced out through the stomata and rises as 
bubbles to the surface of the water. A.t the close of the experiment some 
of the air bubbles will still be in contact with the leaf surface at the opening 
of the stomata. The pressure of the water gradually forces this back into 
the leaf. Other plants will answer for the experiment, but some are more 
suitable than others. 

92a. Number of stomata. — The larger number of stomata are on the 
under side of the leaf. (In leaves which float on the surface of the water 
all of the stomata are on the upper side of the leaf, as in the water lily.) It 
has been estimated by investigation that in general there are 40-300 stomata 
to the square millimeter of surface. In some plants this number is exceeded, 
as in the olive, where there are 625. In an entire leaf of Brassica rapa 
there are about 11,000,000 stomata, and in an entire leaf of the sunflower 
there are about 13,000,000 stomata. 

92b. Amount of water transpired by plants. — The amount of water 
transpired by plants is very great. According to careful estimates a sun- 
flower 6 feet high transpires on the average about one quart per day; an 
acre of cabbages 2,000,000 quarts in four months; an oak tree with 700.000 
leaves transpires about 180 gallons of water per day. According to von Hoh- 
nel, a beech tree no years old transpired about 2250 gallons of water in 
one summer. A hectare of such trees (about 400 on 2.\ acres; would at the 
same rate transpire about 900,000 gallons, or about 30,000 barrels in one 
summer. 



CHAPTER V. 

PATH OF MOVEMENT OF WATER IN PLANTS. 

93. In our study of root pressure and transpiration we have 
seen that large quantities of water or solutions move upwaul 
through the stems of plants. We are now led to inquire 
through what part of the stems the liquid passes in this upward 
movement, or in other words, what is the path of the "sap" as 
it rises in the stem. This we can readily see by the following 
trial. 

94. Place the cut ends of leafy shoots in a solution of some 
of the red dyes. — We may cut off leafy shoots of various plants 
and insert the cut ends in a vessel of water to which have been 
added a few crystals of the dye known as fuchsin to make a deep 
red color (other red dyes may be used, but this one is especially 
good). If the study is made during the summer, the "touch- 
me-not" (impatiens) will be found a very useful plant, or the 
garden -balsam, which may also be had in the winter from con- 
servatories. Almost any plant will do, however, but we should 
also select one like the corn plant (zea mays) if in the summer, 
or the petioles of a plant like caladium, which can be obtained 
from the conservatory. If seedlings of the castor-oil bean are at 
hand we may cut off some shoots which are 8-10 inches high, 
and place them in the solution also. 

95. These solutions color the tracts in the stem and leaves 
through which they flow. — After a few hours in the case of the 
impatiens, or the more tender plants, we can see through che 
stem that certain tracts are colored red by the solution, and 

after 12 to 24 hours there may be seen a red coloration of the 

48 



PA TH OF MO VEMENT. 



49 



leaves of some of the plants used. After the shoots have been 
standing in the solution for a few hours, if we cut them at 
various places we will note that there are several points in the 
section where the tissues are colored red. In the impatiens 
perhaps from four to five, in the sunflower a larger number. In 
these plants the colored areas on a cross section of the stem are 
situated in a concentric ring which separates more or less com- 
pletely an outer ring of the stem from the central portion. If 
we now split portions of the stem lengthwise we see that these 
colored areas continue throughout the length of the stem, in some 
cases even up to the leaves and into them. 

96. If we cut across the stem of a corn plant which has been 
in the solution, we see that instead of the colored areas being in 
a concentric ring they are irregularly scattered, and on splitting 




Fig. 57. 
Broken corn stalk, showing fibro-vascular bundles. 

the stem we see here also that these colored areas extend for long 
distances through the stem. If we take a corn stem which is 
mature, or an old and dead one, cut around through the outer 
hard tissues, and then break the stem at this point, from the 
softer tissue long strings of tissue will pull out as shown in fig. 
57. These strings of denser tissue correspond to the areas 
which are colored by the dye. They are in the form of minute 
bundles, and are called vascular bundles. 



5o 



PHYSIOLOGY. 



97. We thus see that instead of the liquids passing through 
the entire stem they are confined to definite courses. Now that 
we have discovered the path of the upward movement of water 
in the stem, we are curious to see what the structure of these 
definite portions of the stem is. 

98. Structure of the fibro- vascular bundles. — We should now make quite 
thin cross sections, either free hand and mount in water for microscopic 
examination, or they may be made with a microtome and mounted in Canada 
balsam, and in this condition will answer for future study. To illustrate the 
structure of the bundle in one type we may take the stem of the castor-oil 
bean. On examining these cross sections we see that there are groups of 
cells which are denser than the ground tissue. These groups correspond to 
the colored areas in the former experiments, and are the vascular bundles 




Fig. 58. 

Xylem portion of bundle. Cambium portion of bundle. Bast portion of bundle. 

Section of vascular bundle of sunflower stem. 

cut across. These groups are somewhat oval in outline, with the pointed 
end directed toward the center of the stem. If we look at the section 
as a whole we see that there is a narrow continuous ring * of small cells 



* This ring and the bundles separate the stem into two regions, an outer 
one composed of large cells with thin walls, known as the cortical cells, or 
collectively the cortex. The inner portion, corresponding to what is called 
the pith, is made up of the same kind of cells and is called the medulla, or 
pith. When the cells of the cortex, as well as of the pith, remain thin walled 
the tissue is called parenchyma. Parenchyma belongs to the group of 
tissues called fundamental. 



PATH OF MOVEMENT. 5 1 

situated at the same distance from the center of the stem as the middle part 
of the bundles, and that it divides the bundles into two groups of cells. 

99. Woody portion of the bundle. — In that portion of the bundle on the 
inside of die ring, i.e., toward the "pith," we note large, circular, or angu- 
lar cavities. The walls of these cells are quite thick and woody. They are 
therefore called wood cells, and because they are continuous with cells above 
and below them in the stem in such a way that long tubes are formed, they 
are called woody vessels. Mixed in with these are smaller cells, some of 
which also have thick walls and are wood cells. Some of these cells may 
have thin walls. This is the case with all when they are young, and they 
are then classed with the fundamental tissue or soft tissue (parenchyma). 
This part of the bundle, since it contains woody vessels and fibres, is the 
•wood portion of the bundle, or technically the xylem. 

100. Bast portion of the bundle. — If our section is through a part of the 
stem which is not too young, the tissues of the outer part of the bundle will 
show either one or several groups of cells which have white and shiny walls, 
that are thickened as much or more than those of the wood vessels. These 
cells are bast cells, and for this reason this part of the bundle is the bast por- 
tion, or the phloem. Intermingled with these, cells may often be found which 
have thin walls, unless the bundle is very old. Nearer the center of the 
bundle and still within the bast portion are cells with thin walls, angular and 
irregularly arranged. This is the softer portion of the bast, and some of 
these cells are what are called sieve tubes, which can be better seen and 
studied in a longitudinal section of the stem. 

101. Cambium region of the bundle. — Extending across the center of the 
bundle are several rows of small cells, the smallest of the bundle, and we can 
see that they are more regularly arranged, usually in quite regular rows, 
like bricks piled upon one another. These cells have thinner walls than any 
others of the bundle, and they usually take a deeper stain when treated 
with a solution of some of the dyes. This is because they are younger, and 
are therefore richer in protoplasmic contents. This zone of young cells 
across the bundle is the cambium. Its cells grow and divide, and thus increase 
the size of the bundle. ' By this increase in the number of the cells of the 
cambium layer, the outermost cells on either side are continually passing 
over into the phloem, on the one hand, and into the wood portion of the 
bundle, on the other hand. 

102. Longitudinal section of the bundle. — If we make thin longisections of 
the vascular bundle of the castor-oil seedling (or other dicotyledon) so that we 
have thin ones running through a bundle radially, as shown in fig. 59, we 
can see the structure of these parts of the bundle in side view. We see here 
that the form of the cells is very different from what is presented in a cross 
section of the same. The walls of the various ducts have peculiar markings 
on them. These markings are caused by the walls being thicker in some 



52 



PHYSIOLOGY. 



places than in others, and this thickening takes place so regularly in some 
instances as to form regular spiral thickenings. Others have the thickenings 





*ig- 59. 
Longitudinal section of vascular bundle of sunflower stem ; spiral, scalariform and pitted 
vessels at left ; next are wood fibers with oblique cross walls ; in middle are cambium cells 
with straight cross walls, next two sieve tubes, then phloem or bast cells. 

in the form of the rounds of a ladder, while still others have pitted walls or the 

thickenings are in the form of rings. 

103. Vessels or ducts. — One way in which the cells in side view differ 
greatly from an end view, in a cross section in the bundle, is that they are 
much longer in the direction of the axis of the stem. The cells have become 
elongated greatly. If we search for the place where two of these large cells 
with spiral, or ladder-like, markings meet end to end, we see that the 
wall which formerly separated the cells has nearly or quite disappeared. In 
other words the two cells have now an open communication at the ends. 
This is so for long distances in the stem, so that long columns of these large 
cells form tubes or vessels through which the water rises in the stems of 
plants. 

104. In the bast portion of the bundle we detect the cells of the bast fibers 
by their thick walls. They are very much elongated and the ends taper out to 
thin points so that they overla p. In this way they serve to strengthen the stem- 

105. Sieve tubes. — Lying near the bast cells, usually toward the cambium, 
are elongated cells standing end to end, with delicate markings on their cross 
walls which appear like finely punctured plates or sieves. The protoplasm 
in such cells is usually quite distinct, and sometimes contracted away from 
the side walls, but attached to the cross walls, and this aids in the detection 
of the sieve tubes (fig. 59.) The granular appearance which these plates pre- 
sent is caused by minute perforations through the wall so that there is a com- 
munication between the cells. The tubes thus formed are therefore called 
sieve tubes and they extend for long distances through the tube so that there 



PATH OF MOVEMENT. 



53 



is communication throughout the entire length of the stem. (The function of 
the sieve tubes is supposed to be that for the downward transportation of sub- 
stances elaborated in the leaves.) 

106. If we section in like manner the stem of the sunflower we shall see simi- 
lar bundles, but the number is greater than eight. In the garden balsam the 
number is from four to six in an ordinary stem ^-\mm diameter. Here we 
can see quite well the origin of the vascular bundle. Between the larger 
bundles we can see especially in free-hand sections of stems through which 
a colored solution has been lifted by transpiration, as in our former experi- 
ments, small groups of the minute cells in the cambial ring which are colored. 
These groups of cells which form strands running through the stem are pro- 
cambium strands. The cells divide and increase just like the cambium cells, 
and the older ones thrown off on either side change, those toward the center 
of the stem to wood vessels and fibers, and those on the outer side to bast 
cells and sieve tubes. 

107. Fibrovascular bundles in the Indian corn. — We should now make 
a thin transection of a portion of the center of the stem of Indian corn, in 
order to compare the structure of the 
bundle with that of the plants which we 
have just examined. In fig. 6o is repre- 
sented a fibrovascular bundle of the stem 
of the Indian corn. The large cells are 
those of the spiral and reticulated and 
annular vessels. This is the woody por- 
tion of the bundle or xylem, Opposite 
this is the bast portion or phloem, marked 
by the lighter colored tissue at i. The 
larger of these cells are the sieve tubes, 
and intermingled with them are smaller 
cells with thin walls. Surrounding the 
entire bundle are small cells with thick 
walls. These are elongated and the taper- 
ing ends overlap. They are thus slender Transection of fibrovascular bundle of 

and long and form fibers. In such a T t ndian c ° rn - \ t t( \ ward P eri P her y. °{ 
& stem : g, large pitted vessels ; s, spiral 

bundle all of the cambium has passed vessel ; r, annular vessel : /. air cavity 

formed bv breaking apart of the cells ; /, 

over into permanent tissue and is said to fc0 ft bast, a f orm of sieve tissue ; /, thin- 

be closed. walled parenchyma. (Sachs.J 

108. Rise of water in the vessels. — During the movement of the water or 
nutrient solutions upward in the stem the vessels of the wood portion of the 
bundle in certain plants are nearly or quite filled, if root pressure is active 
and transpiration is not very rapid. If. however, on dry days transpiration 
is in excess of root pressure, as often happens, the vessels are not filled with 
the water, but are partly filled with certain gases because the air or other 




54 PHYSIO LOG Y. 

gases in the plant become rarefied as a result of the excessive loss of water. 
There are then successive rows of air or gas bubbles in the vessels separated 
by films of water which also line the walls of the vessels. The condition of 
the vessel is much like that of a glass tube through which one might pass the 
"froth " which is formed on the surface of soapy water. This forms a chain 
of bubbles in the vessels. This chain has been called Jamin's chain because 
of the discoverer. 

109. Why water or food solutions can be raised by the plant to the height 
attained by some trees has never been satisfactorily explained. There are 
several theories propounded which cannot be discussed here. It is probably 
a very complex process. Root pressure and transpiration both play a part, 
or at least can be shown, as we have seen, to be capable of lifting water to a 
considerable height. In addition to this, the walls of the vessels absorb water 
by diffusion, and in the other elements of the bundle capillarity comes also 
into play, as well as osmosis. 

See Organization of Tissues, Chapter 38. 

110. Flow of sap in the spring. — The cause of the bleeding of trees and 
the flow of sap in the spring is little understood. One of the remarkable 
cases is the flow of sap in maple trees. It begins in early spring and ceases 
as the buds are opening, and seems to be initiated by alternation of high 
and low temperatures of day and night. It has been found that the pres- 
sures inside of the tree at this time are enormously increased during the 
day, when the temperature rises after a cold night. This has led to the 
belief that the pressure is caused by the expansion of the gases in the vas- 
cular ducts. The warming up of the twigs and branches of the tree would 
take place rapidly during the day, while the interior of the trunk would be 
only slightly affected. The pressures then would cause the sap to flow 
downward during the day, and at night the branches becoming cool, sap 
would flow back again from the roots and trunk 

Recent experiments by Jones et al. show that while some of the pressure 
is due to the expansion of gas in the tree by the rise of temperature, this 
cannot account for the enormous pressures which are often present, for ex- 
ample, when after a rise in the temperature of 2 C. there was an increase 
of 20 lbs. pressure. 

Then again, after the cessation of the flow in late spring there are often as 
great differences between night and day temperatures. It therefore 
seems reasonable to conclude that the expansion of gases by a rise in tem- 
perature is not the direct cause. 

Activities of the cells. — It has been suggested by some that the rise in 
temperature exercises an influence on the protoplasts, or living cells, so 
that they are stimulated to a special activity resulting in an exudation pres- 
sure from the individual cells ? which is known to take place. With the fall of 



PATH OF MOVEMENTS, 55 

temperature at night this activity would cease and there might result a 
lessened pressure in the cells. Since the specific activities of cells are 
known to vary in different plants, and in the same plant at different 
seasons, some support is gained for this theory, though it is generally 
believed that the activities of the living cells in the stems are not necessary 
for the upward flow of water. It must be admitted, however, that at 
present we know very little about this interesting problem. 



CHAPTER VI. 

MECHANICAL USES OF WATER. 

111. Turgidity of plant parts. — As we have seen by the 
experiments on the leaves, turgescence of the cells is one of the 
conditions which enables the leaves to stand out from the stem, 
and the lamina of the leaves to remain in an expanded position, 
so that they are better exposed to the light, and to the currents 
of air. Were it not for this turgidity the leaves would hang 
down close against the stem. 

112. Restoration of turgidity in shoots. — If we cut off a 
living stem of geranium, coleus, tomato, or " balsam," and allow 
the leaves to partly wilt so that the shoot loses its turgidity, it is 
possible for this shoot to regain turgidity. The end may be 
freshly cut again, placed in a vessel of water, covered with a bell 
jar and kept in a room where the temperature 
is suitable for the growth of the plant. The 
shoot will usually become turgid again from 
the water which is absorbed through the cut 
end of the stem and is carried into the leaves 
where the individual cells become turgid, and 
the leaves are again expanded. Such shoots, 
and the excised leaves also, may often be made 
turgid again by simply immersing them in 
water, as one of the experiments with the salt 
solution would teach. 




Fig. 61. 

Restoration of turgidity 

(Sachs). 



113. Turgidity may be restored more certainly and 
quickly in a partially wilted shoot in another way. 
The cut end of the shoot may be inserted in a U tube as shown in fig. 61, the 
end of the tube around the stem of the plant being made air-tight. The arm 

56 



TURGESCENCE. 57 

of the tube in which the stem is inserted is filled with water and the water is 
allowed to partly fill the other arm. Into this other arm is then poured 
mercury. The greater weight of the mercury causes such pressure upon the 
water that it is pushed into the stem, where it passes up through the vessels 
in the stems and leaves, and is brought more quickly and surely to the cells 
which contain the protoplasm and cell-sap, so that turgidity is more quickly 
and certainly attained. 

114. Tissue tensions. — Besides the turgescence of the cells of 
the leaves and shoots there are certain tissue tensions without 
which certain tender and succulent shoots, etc., would be limp, 
and would droop. There are a number of plants usually accessi- 
ble, some at one season and some at others, which may be used 
to illustrate tissue tension. 

115. Longitudinal tissue tension. — For this in early summer 
one may use the young and succulent shoots of the elder 
(sambucus); or the petioles of rhubarb during the summer and 
early autumn ; or the petioles of richardia. Petioles of cala- 
dium are excellent for this purpose, and these may be had at 
almost any season of the year from the greenhouses, and are 
thus especially advantageous for work during late autumn or 
winter. The tension is so strong that a portion of such a 
petiole 10— 15cm long is ample to demonstrate it. As we grasp 
the lower end of the petiole of a caladium, or rhubarb leaf, we 
observe how rigid it is, and how well it supports the heavy 
expanded lamina of the leaf. 

116. The ends of a portion of such a petiole or other object 
which may be used are cut off squarely. With a knife a strip 
from 2—T > mm in thickness is removed from one side the full 
length of the object. This strip we now find is shorter than 
the larger part from which it was removed. The outer tissue 
then exerts a tension upon the petiole which tends to shorten 
it. Let us remove another strip lying next this one, and 
another, and so on until the outer tissues remain only upon 
one side. The object will now bend toward that side. Now 
remove this strip and compare the length of the strips re- 
moved with the central portion. We find that they are much 



58 



PHYSIOLOG Y. 



shorter now. In other words there is also a tension in the tissue 
of the central portion of the petiole, the direction of which is 
opposite to that of the superficial tissue. The parts of the petiole 
now are not rigid, and they easily bend. These two longitudi- 
nal tissue tensions acting in opposition to each other therefore 
give rigidity to the succulent shoot. It is only when the indi- 
vidual cells of such shoots or petioles are turgid that these tissue 
tensions in succulent shoots manifest themselves or are promi- 
nent. 

117. To demonstrate the efficiency of this tension in giving support, let us 
take a long petiole of caladium or of rhubarb. Hold it by one end in a hori- 
zontal position. It is firm and rigid, and does not droop, or but little. Re- 
move all of the outer portion of the tissues, as described above, leaving only 
the central portion. Now attempt to hold it in a horizontal position by one 
end. It is flabby and droops downward because the longitudinal tension is 
removed. 

118. Longitudinal tension in dandelion stems. — Take long 

and fresh dandelion stems. Split 
them. Note that they coil. The 
longitudinal tension is very great. 
Place some of these strips in 
fresh water. They coil up into 
close curls because by the ab- 
sorption of water by the cells the 
turgescence of the individual cells 
is increased, and this increases 
the tension in the stem. Now 
place them in salt water (a 5 per 
cent solution). Why do they 
uncoil ? 

119. To imitate the coiling 
of a tendril. — Cut out a narrow 
strip from a long dandelion stem. 

Strip from dTndeHon stem made to Fasten to a piece of Soft wood, 
imitate a plant tendril. ^.^ ^ endg dose togetherj as 

shown in fig. 62. Now place it in fresh water and watch it coil. 
Part of it coils one way and part another way, just as a ten- 




tf@M^J 




Fig. 62. 



MECHANICAL USES OF WATER. 59 

dril does after the free end has caught hold of some place for 
support. 

120. Transverse tissue tension. — To illustrate this one may 
take a willow shoot 3-5CW in diameter and saw off sections about 
2cm long. Cut through the bark on one side and peel it off in a 
single strip. Now attempt to replace it. The bark will not 
quite cover the wood again, since the ends will not meet. It 
must then have been held in transverse tension by the woody 
part of the shoot. 



CHAPTER VII. 

STARCH AND SUGAR FORMATION. 
1 . The Gases Concerned. 



121. Gas given off by green plants in the sunlight. — Let 

us take some green alga, like spirogyra, which is in a fresh con- 
dition, and place one lot in a beaker or tall glass vessel of water 
and set this in the direct sunlight or in a well lighted place. At 
the same time cover a similar vessel 
of spirogyra with black cloth so that 
it will be in the dark, or at least in 
very weak light. 

122. In a short time we note that in 
the first vessel small bubbles of gas are 
accumulating on the surface of the 
threads of the spirogyra, and now and 
then some free themselves and rise to 
the surface of the water. Where there 
is quite a tangle of the threads the gas 
is apt to become caught and held back 
in larger bubbles, which on agitation of 
the vessel are freed. 

If We now examine the Second Vessel Oxygen gas given off by spirogyra 

we see that there are no bubbles, or only a very few of them. 
We are led to believe then that sunlight has had something to 
do with the setting free of this gas from the plant. 

123o We may now take another alga like vaucheria and per- 
form the experiment in the same way, or to save time the 
two may be set up at once. In fact if we take any of the green 




SEARCH FORMATION: THE GASES. 6 1 

dlgas cuid treat them as described above gas will be given off in a 
similar manner. 

124. We may now take one of the higher green plants, an 
aquatic plant like elodea, callitriche, etc. Place the plant in 
m the water with the cut end of the stem uppermost, 
tf& k i^ . — -/* but still immersed, the plant being weighted down 
by a glass rod or other suitable object. If we 
place the vessel of water containing these leafy 
stems in the bright sunlight, in a short time bub- 
bles of gas will pass off quite rapidly from the cut 
end of the stem. If in the same vessel we 
^mmmm^^g^ place another stem, from which the leaves 
■^■L W h ave been cut, the number of bubbles of gas 

x> uui* lg 'r 64 * given off will be very few. This indicates that 

Bubbles of oxygen gas ° J 

given off from elodea in a i ar pr e part of the gas is furnished by the 

presence of sunlight. ° r ° J 

(° els ^ leaves. 

125. Another vessel fitted up in the same way should be placed in the 
dark or shaded by covering with a box or black cloth. It will be seen here, 
as in the case of spirogyra, that very few or no bubbles of gas will be set 
free. Sunlight here also is necessary for the rapid escape of the gas. 

126. We may easily compare the rapidity with which light of varying 
intensity effects the setting free of this gas. After cutting the end of the stem 
let us plunge the cut surface several times in melted paraffine, or spread 
over the cut surface a coat of varnish. Then prick with a needle a small 
hole through the paraffine or varnish. Immerse the plant in water and 
place in sunlight as before. The gas now comes from the puncture through 
the coating of the cut end, and the number of bubbles given off during a 
given period can be ascertained by counting. If we duplicate this experi- 
ment by placing one plant in weak light or diffused sunlight, and another in 
the shade, we can easily compare the rapidity of the escape of the gas under 
the different conditions, which represent varying intensities of light. We 
see then that not only is sunlight necessary for the setting free of this gas, but 
that in diffused light or in the shade the activity of the plant in this respect 
is less than in direct sunlight. 

127. What this gas is. — If we take quite a quantity of the 
plants of elodea and place them under an inverted funnel 
which is immersed in water, the gas will be given off in quite 
large quantities and will rise into the narrow exit ot the funnel. 



62 



PHYSIOLOGY. 




The funnel should be one with a short tube, or the vessel one 
which is quite deep so that a small test tube which is filled with 
water may in this condition be inverted over the 
opening of the funnel tube. With this arrange- 
ment of the experiment the gas will rise in the 
inverted test tube, slowly displace a portion of 
the water, and become collected in a sufficient 
quantity to afford us a test. When a consider- 
able quantity has accumulated in the test tube, we 
may close the end of the tube in the water with 
the thumb, lift it from the water and invert. A Flg - 65 ' 

Apparatus for col- 

The gas will rise against the thumb. A dry Acting quantity of 

° J oxygen from elodea. 

soft pine splinter should be then lighted, and (Detmer.) 
after it has burned a short time, extinguish the flame by blowing 
upon it, when the still burning end of the splinter should be 
brought to the mouth of the tube as the thumb is quickly moved 
to one side. The glowing of the splinter shows that the gas is 
oxygen. 

128. It is better to allow the apparatus to stand several days 

in the sunlight in order to 
catch a full tube of the gas. 
Or on a sunny day carbon 
dioxide gas can be led into 
the water in the jar from 
a generator, such an one 
used for the evolution of 
The C0 2 can be produced 
by the action of hydrochloric acid 
on bits of marble. The C0 2 
should not be run below the fun- 
nel. The test-tube should be 
fastened so that the light oxygen 
gas will not raise it off the fun- 
nel. With the tube full of gas the 
Readytosfewhat'thegasis. test for oxygen can be made by 
lifting the tube with one hand and 





STARCH FORMATION — THE GASES. 63 

quickly thrusting the glowing end of the splinter in with the 
other hand. If properly 
handled, the splinter will 
flame again. If it is neces- 
sary to keep the appa- 
ratus standing for more 

than one day it is Well The splinter lights again in the presence of 

oxygen gas. 

to add fresh water in the 

place of most of the water in the jar. Do not use leaves of land 
plants in this experiment, since the bubbles which rise when these 
leaves are placed in water are not evidence that this process is 
taking place. 

■ 129. Oxygen given off by green land plants also. — If we should extend 
our experiments to land plants we should find that oxygen is given off by 
them under these conditions of light. Land plants, however, will not do 
this when they are immersed in water, but it is necessary to set up rather 
complicated apparatus and to make analyses of the gases at the beginning 
and at the close of the experiments. This has been done, however, in a suffi- 
cientlv large number of cases so that we know that all green plants in the 
sunlight, if temperature and other conditions are favorable, give off oxygen. 

130. Absorption of carbon dioxide. — We have next to inquire 
where the oxygen comes from which is given off by green plants 
when exposed to the sunlight, and also to learn something more 
of the conditions necessary for the process. We know that 
water which has been for some time exposed to the air and soil, 
and has been agitated, like running water of streams, or the 
water of springs, has mixed with it a considerable quantity of 
oxygen and carbon dioxide. 

If we boil spring water or hydrant water which comes from 
a stream containing oxygen and carbon dioxide, for about 20 
minutes, these gases are driven off. We should set this aside 
where it will not be agitated, until it has cooled sufficiently to 
receive plants without injury. Let us now place some spirogyra 
or vaucheria, and elodea, or other green water plant, in this 
boiled water and set the vessel in the bright sunlight under the 
same conditions which were employed in the experiments for the 
evolution of oxygen. No oxygen is given off. 



64 PHYSIOLOGY. 

Can it be that this is because the oxygen was driven from 
the water in boiling? We shall see. Let us take the vessel 
containing the water, or some other boiled water, and agitate it 
so that the air will be thoroughly mixed with it. In this way 
oxygen is again mixed with the water. Now place the plant 
again in the water, set in the sunlight, and in several minutes 
observe the result. No oxygen or but little is given off. There 
must be then some other requisite for the evolution of the oxygen. 

132. The gases are interchanged in the plants. — We will now 
introduce carbon dioxide again in the water. This can be done 
by leading C0 2 from a gas generator into the water. Broken 
bits of marble are placed in the generator, acted upon by hydro- 
chloric acid, and the gas is led over by glass tubing. Now if we 
place the plant in the water and set the vessel in the sunlight, in 
a few minutes the oxygen is given off rapidly. 

133. A chemical change of the gas takes place within the 
plant cell. — This leads us to believe then that C0 2 is in some 
way necessary for the plant in this process. Since oxygen is 
given off while carbon dioxide, a different gas, is necessary, it 
would seem that a chemical change takes place in the gases 
within the plant. Since the process takes place in such simple 
plants as spirogyra as well as in the more bulky and higher 
plants, it appears that the changes go on within the cell, in fact 
within the protoplasm. 

134. Gases as well as water can diffuse through the proto- 
plasmic membrane. — Carbon dioxide then is absorbed by the 
plant while oxygen is given off. We see therefore that gases as 
well as water can diffuse through the protoplasmic membrane of 
plants under certain conditions. 

2. Where Starch is Formed. 

We have found by these simple experiments that some 
chemical change takes place within the protoplasm of the green 
cells of plants during the absorption of carbon dioxide and the 
giving off of oxygen. We should examine some of the green 
parts of those plants used in the experiments, or if they are not 



STARCH: PHOTOSYNTHESIS. 65 

at hand we should set up others in order to make this examina- 
tion. 

135. Starch formed as a result of this process. — We may take 
spirogyra which has been standing in water in the bright sun- 
light for several hours. A few of the threads should be placed 
in alcohol for a short time to kill the protoplasm. From the 
alcohol we transfer the threads to a solution of iodine in potas- 
sium iodide. We find that at certain points in the chlorophyll 
band a bluish tinge, or color, is imparted to the ring or sphere 
which surrounds the pyrenoid. In our first study of the spirogyra 
cell we noted this sphere as being composed of numerous small 
grains of starch which surround the pyrenoid. 

136. Iodine used as a test for starch. — This color reaction 
which we have obtained in treating the threads with iodine is 
the well-known reaction, or test, for starch. We have demon- 
strated then that starch is present in spirogyra threads which 
have stood in the sunlight with free access to carbon dioxide. 

If we examine in the same way some threads which have stood 
in the dark for a few days we obtain no reaction for starch, or at 
best only a slight reaction. This gives us some evidence that a 
chemical change does take place during this process (absorption 
of C0 2 and giving off of oxygen), and that starch is a product of 
that chemical change. 

137. Schimper's method of testing for the presence of starch. 
— Another convenient and quick method of testing for the pres- 
ence of starch is what is known as Schimper's method. A 
strong solution of chloral hydrate is made by taking 8 grams of 
chloral hydrate for every $cc of water. To this solution is added 
a little of an alcoholic tincture of iodine. The threads of spi- 
rogyra may be placed directly in this solution, and in a few 
moments mounted in water on the glass slip and examined with 
the microscope. The reaction is strong and easily seen. 

We should also examine the leaves of elodea, or one of 
the higher green plants which has been for some time in the 
sunlight. We may use here Schimper's method by placing the 
leaves directly in the solution of chloral hydrate and iodine. 



66 



PHYSIOLOGY. 



The leaves are made transparent by the chloral hydrate so that 
the starch reaction from the iodine is easily detected. 

The following is a convenient and safe method of extract- 
ing chlorophyll from leaves. Fill a large pan, preferably a 
dishpan, half full of hot water. This may be kept hot by a 
small flame. On the water float an evaporating dish partly 
filled with alcohol. The leaves should be first immersed in 
the hot water for several minutes, then placed in the alcohol, 
which will quickly remove the chlorophyll. Now immerse the 
leaves in the iodine solution. 

138. Green parts of plants form starch when exposed to 
light. — Thus we find that in the case of all the green plants we 
have examined, starch is present in the green cells of those which 




Fig. 68. Fig. 69. 

Leaf of coleus showing green and white Similar leaf treated with iodine, the starch 
areas, before treatment with iodine. reaction only showing where the leaf 

was green. 

have been standing for some time in the sunlight where the proc- 
ess of the absorption of C0 2 and the giving off of oxygen can 
go on, and that in the case of plants grown in the dark, or in 



STARCH AND SUGAR: CHLOROPHYLL. 6j 

leaves of plants which have stood for some time in the dark, 
starch is absent. We reason from this that starch is the product 
of the chemical change which takes place in the green cells 
under these conditions. The C0 2 which is absorbed by the 
plant mixes with the water (H 2 0) in the cell and immediately 
forms carbonic acid. The chlorophyll in the leaf absorbs radi- 
ant energy from the sun which splits up the carbonic acid, and 
its elements then are put together into a more complex com- 
pound, starch. This process of putting together the elements 
of an organic compound is a synthesis, or a synthetic assimila- 
tion, since it is done by the living plant. It is therefore a syn- 
thetic assimilation of carbon dioxide. Since the sunlight sup- 
plies the energy it is also called photosynthesis, or photo synthetic 
assimilation. We can also say carbon dioxide assimilation, or 
C0 2 assimilation (see paragraph on assimilation at close of 
Chapter 10). 

139. Starch is formed only in the green parts of variegated 
leaves. — If we test for starch in variegated leaves like the leaf of 
a coleus plant, we shall have an interesting demonstration of the 
fact that the green parts of plants only form starch. We may 
take a leaf which is partly green and partly white, from a plant 
which has been standing for some time in bright light. Fig. 68 
is from a photograph of such a leaf. We should first boil it in 
alcohol to remove the green color. Now immerse it in the 
potassium iodide of iodine solution for a short time The parts 
which were formerly green are now dark blue or nearly black, 
showing the presence of starch in those portions of the leaf, 
while the white part of the leaf is still uncolored. This is well 
shown in fig. 69, which is from a photograph of another coleus 
leaf treated with the iodine solution. 

3. Chlorophyll and the Formation of Starch. 

140. In our experiments thus far in treating of the absorption 
of carbon dioxide and the evolution of oxygen, with the accom- 
panying formation of starch, we have used green plants. 



6$ PHYSIOLOG V. 

141. Fungi cannot form starch. — If we should extend our 
experiments to the fungi, which lack the green color so charac- 
teristic of the majority of plants, we should find that photosyn- 
thesis does not take place even though the plants are exposed 
to direct sunlight. These plants cannot then form starch, but 
obtain carbohydrates for food from other sources. 

142. Photosynthesis cannot take place in etiolated plants. — 
Moreover photosynthesis is usually confined to the green plants, 
and if by any means one of the ordinary green plants loses its 
green color this process cannot take place in that plant, even 
when brought into the sunlight, until the green color has ap- 
peared under the influence of light. 

This may be very easily demonstrated by growing seedlings 
of the bean, squash, corn, pea, etc. (pine seedling? are green even 
when grown in the dark), in a dark room, or in a dark receiver 
of some kind which will shut out the rays of light. The room 
or receiver must be quite dark. As the seedlings are " coming 
up," and as long as they remain in the dark chamber, they will 
present some other color than green; usually they are somewhat 
yellowed. Such plants are said to be etiolated. If they are 
brought into the sunlight now for a few hours and then tested 
for the presence of starch the result will be negative. But if the 
plant is left in the light, in a few days the leaves begin to take 
on a green color, and then we find that carbon dioxide assimila- 
tion begins. 

143. Chlorophyll and chloroplasts. — The green substance in 
plants is then one of the important factors in this complicated 
process of forming starch. This green substance is chlorophyll, 
and it usually occurs in definite bodies, the chlorophyll bodies, 
or chloroplasts. 

The material for new growth of plants grown in the dark is derived from 
the seed. Plants grown in the dark consist largely of water and protoplasm, 
the walls being very thin. 

144. Form of the chlorophyll bodies. — Chlorophyll bodies 
vary in form in some different plants, especially in some of the 



STARCH AND SUGAR: CHLOROPHYLL. 



6 9 



lower plants. This we have already seen in the case of 
spirogyra, where the chlorophyll body is in the form of a very 
irregular band, which courses around the inner side of the cell 
wall in a spiral manner. In zygnema, which is related to 
spirogyra, the chlorophyll bodies are star-shaped. In the 
desmids the form varies greatly. In cedogonium, another of 
the thread-like algae, illustrated in fig. 144, the chlorophyll bodies 




Fig. 69a. 
Section of ivy leaf, palisade cells above, loose parenchyma, with large intercellular spaces 
in center. Epidermal cells on either edge, with no chlorophyll bodies. 

are more or less flattened oval disks. In vaucheria, too, a 
branched thread-like alga shown in fig. 138, the chlorophyll 
1 bodies are oval in outline. These two plants, oedogonium and 
vaucheria, should be examined here if possible, in order to be- 
come familiar with their form, since they will be studied later 
under morphology (see chapters on OLdogonium and vaucheria, 
iOr the occurrence and form of these plants). The form of the 
chlorophyll body found in oedogonium and vaucheria is that 
which is common to many of the green algae, and also occurs in 
the mosses, liverworts, ferns, and the higher plants. It is a 
more or less rounded, oval, flattened body. 

145. Chlorophyll is a pigment which resides in the chloroplast. — That 
the chlorophyll is a coloring substance which resides in the chloroplastid, 
and docs not form the body itself, can be demonstrated by dissolving out the 
chlorophyll when the framework of the chloroplastid is apparent. The 
green parts of plants which have been placed for some time in alcohol lose 



7° PHYSIOLOGY. 

their green color. The alcohol at the same time becomes tinged with green. 
In sectioning such plant tissue we find that the chlorophyll bodies, or chloro- 
plastids as they are more properly called, are still intact, though the green 
color is absent. From this we know that chlorophyll is a substance distinct 
from that of the chloroplastid. 

146. Chlorophyll absorbs energy from sunlight for photosynthesis. — It 
has been found by analysis with the spectroscope that chlorophyll absorbs cer- 
tain of the rays of the sunlight. The energy which is thus obtained from 
the sun, called kinetic energy, acts on the molecules of CH 2 3 , separating 
them into molecules of C, H, and O. (When the C0 9 from the air enters 
the plant cell it immediately unites with some of the water, forming carbonic 
acid = CH 2 3 . ) After a series of complicated chemical changes starch is 
formed by the union cf carbon, oxygen, and hydrogen. In this process of 
the reduction of the CH./) 3 and the formation of starch there is a surplus of 
oxygen, which accounts for the giving off of oxygen during the process. 

147. Rays of light concernel in photosynthesis. — If a solution of 
chlorophyll be made, and light be passed through it, and this light be 
examined with the spectroscope, there appear what are called absorption bands. 
These are dark bands which lie across certain portions of the spectrum. 
These bands lie in the red, orange, yellow, green, blue, and violet, but the 
bands are stronger in the red, which shows that chlorophyll absorbs more of 
the red rays of light than of the other rays. These are the rays of low 
refrangibility. The kinetic energy derived by the absorption of these rays 
of light is transformed into potential energy. That is, the molecule of 
CH 2 O a is broken up, and then by a different combination of certain elements 
starch is formed.* 

148. Starch grains formed in the chloroplasts. — During photosynthesis the 
starch formed is deposited generally in small grains within the green chloro- 
olast in the leaf. We can see this easily by examining the leaves of some 
moss like funaria which has been in the light, or in the chloroplasts cf the 
prothallia of ferns, etc. Starch grains may also be formed in the chloro- 
plasts from starch which was formed in some other part of the plant, but 



* In the formation of starch during photosynthesis the separated mole- 
cules from the carbon dioxide and water unite in such a way that carbon, 
hydrogen, and oxygen are united into a molecule of starch. This result is 
usually represented by the following equation: C0 2 +H 2 = CH 2 + 2 . 
Then by polymerization 6(CH 2 0) = C 6 H 12 6 = grape sugar. Then 
C f H, 2 6 — H 2 = CgHj.Og = starch. It is believed, however, that the 
process is much more complicated than this, that several different com- 
pounds are formed before starch finally appears, and that the formula for 
Starch js much higher numerically than is represented by C^H^O^. 



STARCH AND SUGAR; CHLOROPHYLL. 7 1 

which has passed in solution. Thus the functions of the chloroplast are 
twofold, that of photosynthesis and the formation of starch grains. 

149. In the translocation of starch when it becomes stored up in various 
parts of the plant, it passes from the state of solution into starch grains in 
connection with plastids similar to the chloroplasts, but which are not green. 
The green ones are sometimes called chloroplasts, while the colorless ones 
are termed leucoplasts, and those possessing other colors, as red and yellow, 
in floral leaves, the root of the carrot, etc., are called chromoplasts. 

150. Photosynthesis in other than green plants. — While carbohydrates 
are usually only formed by green plants, there are some exceptions. Ap- 
parent exceptions are found in the blue-green algae, like oscillatoria, nostoc, 
or in the brown and red sea weeds like fucus, rhabdonia, etc. These plants, 
however, possess chlorophyll, but it is disguised by another pigment or 
color. There are plants, however, which do not have chlorophyll and yet 
form carbohydrates with evolution of oxygen in the presence of light, as 
for example a purple bacterium, in which the purple coloring substance 
absorbs light, though the rays absorbed most energetically are not the 
red. 

151. Influence of light on the movement of chlorophyll bodies. — In fern 
prothallia. — If we place fern prothallia in weak light for a few hours, and 
then examine them under the microscope, we find that the most of the chloro- 
phyll bodies in the cells are arranged along the inner surface of the hori- 
zontal wall. If now the same prothallia are placed in a brightly lighted 
place for a short time most of the chlorophyll bodies move so that they are 




Fig. 70. Fig. 71. 

Cell exposed to weak diffused light Same cell exposed to strong light, 

showing chlorophyll bodies along the showing chlorophyll bodies have 

horizontal walls. moved to perpendicular walls. 

Figs. 70, 71. — Cell of prothallium of fern. 

arranged along the surfaces of the perpendicular walls, and instead of hav- 
ing the flattened surfaces exposed to the light as in the former case, the 
edges of the chlorophyll bodies are now turned toward the light. (See figs. 



7 2 PHYSIOLOG Y. 

70, 71.) The same phenomenon has been observed in many plants. Light 
then has an influence on chlorophyll bodies, to some extent determining 
their position. In weak light they are arranged so that the flattened sur- 
faces are exposed to the incidence of the rays of light, so that the chloro- 
phyll will absorb as great an amount as possible of kinetic energy; but 
intense light is stronger than necessary, and the chlorophyll bodies move so 
that their edges are exposed to the incidence of the rays. This movement 
of the chlorophyll bodies is different from that which takes place in some 
water plants like elodea. The chlorophyll bodies in elodea are free in the 
protoplasm. The protoplasm in the cells of elodea streams around the 
inside of the cell wall much as it does in nitella and the chlorophyll bodies 
are carried along in the currents, while in nitella they are stationary. 



CHAPTER VIII. 



STARCH AND SUGAR CONCLUDED. 
PLANT SUBSTANCE. 



ANALYSIS OF 



1 . Translocation of Starch. 



152. Translocation of starch. — It has been found that leaves of many 
plants grown in the sunlight contain starch when examined after being in 
the sunlight for several hours. But when the plants are left in the dark for 
a day or two the leaves contain no starch, or a much smaller amount. This 
suggests that starch after it has been formed may be transferred from the 
leaves, or from those areas of the leaves where it has been formed. 

To test this let us perform an experiment which is often made. We 
may take a plant such as a 
garden tropaeolum or a clover 
plant, or other land plant in 
which it is easy to test for the 
presence of starch. Pin a 
piece of circular cork, which 
is smaller than the area of 
the leaf, on either side of the 
leaf, as in fig. 72, but allow 
free circulation of air between 
the cork and the under side of 
the leaf. Place the plant 
where it will be in the sunlight. 
On the afternoon of the fol- 
lowing day, if the sun has been shining, test the entire leaf for starch. The 
part covered by the cork will not give the reaction for starch, as shown by 
the absence of the bluish color, while the other parts of the leaf will show it. 
The starch which was in that part of the leaf the day before was dissolved 
and removed during the night, and then during the following day, the 
parts being covered from the light, no starch was formed in them. 

73 




Fig. 72. 
Leaf of tropaeolum 
with pi >rtion covered 
with corks to pre- 
vent the formation 
of starch. (After 
Detmer.) 



Fig. 73- 
Leaf of tropaeolum treated 
with iodine after removal of 
cork, to show that starch is 
removed from the leaf dur- 
ing the night. 



74 PHYSIO LOG Y. 

153. Starch in other parts of plants than the leaves. — We 

may use the iodine test to search for starch in other parts of 
plants than the leaves. If we cut a potato tuber, scrape some of 
the cut surface into a pulp, and apply the iodine test, we obtain 
a beautiful and distinct reaction showing the presence of starch. 
Now we have learned that starch is only formed in the parts 
containing chlorophyll. We have also learned that the starch 
which has been formed in the leaves disappears from the leaf or 
is transferred from the leaf. We judge therefore that the starch 
which we have found in the tuber of the potato was formed first 
in the green leaves of the plant, as a result of photosynthesis. 
From the leaves it is transferred in solution to the underground 
stems, and stored in the tubers. The starch is stored here by 
the plant to provide food for the growth of new plants from the 
tubers, which are thus much more vigorous than the plants 
would be if grown from the seed. 

154. Form of starch grains. — Where starch is stored as a reserve material 
it occurs in grains which usually have certain characters peculiar to the 
species of plant in which they are found. They vary in size in many 
different plants, and to some extent in form also. If we scrape s^e of 
the cut surface of the potato tuber into a pulp and mount a sniaii ijiuininy 
in water, or make a thin section for microscopic examination, we find 
large starch grains of a beautiful structure. The grains are oval in 
form and more or less irregular in outline. But the striking peculiarity is 
the presence of what seem to be alternating dark and light lines in the starch 
grain. We note that the lines form irregular rings, which are smaller 
and smaller until we come to the small central spot termed the " hilum " of 
the starch grain. It is supposed that these apparent lines in the starch 
grain are caused by the starch substance being deposited in alternating dense 
and dilute layers, the dilute layers containing more water than the dense 
ones; others think that the successive layers from the hilum outward are 
regularly of diminishing density, and that this gives the appearance of alter- 
nating lines. The starch formed by plants is one of the organic substances 
which are manufactured by plants, and it (or glucose) is the basis for the 
formation of other organic substances in the plant. Without such organic 
substances green plants cannot make any appreciable increase of plant 
substance, though a considerable increase in size of the plant may take 
place. 

Note. — The organic compounds resulting from photosynthesis, since 
thev are formed by the union of carbon, hydrogen, and oxygen in such a 
way that the hydrogen and oxygen arc usually present in the same propor- 



STARCH: TRANSLOCATION. 75 

tion as in water, are called carbohydrates. The most common carbo- 
hydrates are sugars (cane sugar, C 12 H 22 O u , for example, in beet roots, 
sugar cane, sugar maple, etc.), starch, and cellulose. 

155. Vaucheria. — The result of carbon dioxide assimilation in the 
threads of Vaucheria is not clearly understood. Starch is absent or diffi- 
cult to find in all except a few species, while oil globules are present in 
most species. These oil globules are spherical, colorless, globose and 
highly refringent. Often small ones are seen lying against chlorophyll 
bodies. Oil is a hydrocarbon (containing C, H, and O, but the H and O 
are in different proportions from what they are in H 2 0) and until recently 
it was supposed that this oil in Vaucheria was the direct result of photo- 
synthesis. But the oil does not disappear when the plant is kept for a 
long time in the dark, which seems to show that it is not the direct prod- 
uct of carbon dioxide assimilation, and indicates that it comes either from 
a temporary starch body or from glucose. Schimper found glucose in sev- 
eral species of Vaucheria, and Waltz says that some starch is present in 
Vaucheria sericea, while in V. tuberosa starch is abundant and replaces the 
oil. To test for oil bodies in Vaucheria treat the threads with weak osmic 
acid, or allow them to stand for twenty-four hours in Fleming's solution 
(which contains osmic acid). Mount some threads and examine with 
microscope. The oil globules are stained black. 

2. Sugar, and Digestion of Starch.* 

156. It is probable that some form of sugar is always produced as the 
result of photosynthesis. The sugar thus formed may be stored as such 
or changed to starch. In general it may be said that sugar is most com- 
mon in the green parts of monocotyledonous plants, while starch is most 
frequent in dicotyledons. Plant sugars are of three general kinds: cane 
sugar abundant in the sugar cane, sugar beet, sugar maple, etc.; glucose 
and fruit sugar, found in the fruits of a majority of plants, and abundant 
in some, as in apples, pears, grapes, etc.; and maltose, a variety produced 
in germinating seeds, as in malted barley. 

157. Test for sugar. — A very pretty experiment maybe made by taking 
two test tubes, placing in one a solution of commercial grape sugar (glucose), 
in the other one of granulated cane sugar, and adding to each a few drops 
of PVhling's solution. f After these tubes have stood in a warm place for 



* Paragraphs 156-160 were prepared by Dr. E. J. Durand. 
f Make up three stock solutions as follows: 

(T) 

Copper sulphate 9 grams 

Water 250 cc, 



7 6 PHYSIO LOG Y. 

half an hour, it will be found that a bright orange brown or cinnabar- 
colored precipitate of copper and cuprous oxide has formed in the tube 
containing grape sugar, while the other solution is unchanged. Grape 
sugar or glucose, therefore, reduces Fehling's solution, while cane sugar 
as such has no effect upon it. 

Cane sugar may be changed or converted to glucose by being boiled for 
a short time with a dilute acid, or by adding Fehling's solution to the sugar 
solution and boiling. In the latter case the change is brought about by 
the alkali and the precipitate of copper and cuprous oxide forms. 

158. Tests for sugar in plant tissue. — (a) Scrape out a little of the tissue 
from the inside of a ripe apple or pear, place it with a little water in a test 
tube, and add a few drops of Fehling's solution. After standing half an 
hour the characteristic precipitate of copper and cuprous oxide appears, 
showing that grape sugar is present in quantity. 

Make thin sections of the apple and mount in a drop of Fehling's solu- 
tion on a slide. After half an hour examine with the microscope. The 
granules of cuprous oxide are present in the cells of the tissue in great 
abundance. 

(b) Cut up several leaves of a young vigorous corn seedling, cover with 
water in a test tube and boil for a minute. After the decoction has cooled 
add the Fehling's solution and allow to stand. The precipitate will ap- 
pear. For comparison take similar corn leaves, remove the chlorophyll 
with alcohol and test with iodine. No starch reaction appears. The car- 
bohydrate in corn leaves is therefore glucose and not starch. Tf now the 
corn seed be examined the cells will be found to be full of starch grains 
which give the beautiful blue reaction with iodine. This experiment shows 
that grape sugar is formed in the leaves of the corn plant, but is changed to 
starch when stored in the seed. 

(c) Take two leaves of bean seedling or coleus, test one for sugar and 
the other for starch. Both are present. 

(d) Procure some maple sap in the spring, or in the winter months make 
a decoction of the broken tips of young branches of the sugar maple by 
boiling them in water in a test tube. To the sap or cool decoction add 
Fehling's solution. No precipitate appears after standing. Now heat 

Caustic potash 30 grams 

Water. . 250 cc. 

(3) 

Rocbelle salts. * , . 49 grams 

Water 250 cc. 

For Fehling's solution take one volume of each of (1), (2), and (3), and 
to the mixture add two volumes of water. 



SUGAR : DIGESTION OF STARCH. 77 

the same solution to the boiling-point, and the precipitate forms, showing 
the presence of cane sugar in the maple sap which was converted to glu- 
cose and fruit sugar by boiling in the presence of an alkali. 

(e) Scrape out some of the tissue from a sugar beet root, cover with 
water in a test tube and add Fehling's solution. No change takes place 
after standing. Boil the same solution and the precipitate forms, showing 
the presence of cane sugar, inverted to grape sugar and fruit sugar by the 
hot alkali. 

159. How starch is changed to sugar.— We have seen that in many plants 
the carbohydrate formed as the result of carbon dioxide assimilation is 
stored as starch. This substance being insoluble in water must be changed 
to sugar, which is soluble before it can be used as food or transported to 
other parts of the plant. This is accomplished through the action of cer- 
tain enzymes, principallv diastase. This substance has the power of act- 
ing upon starch under proper conditions of temperature and moisture, 
causing it to take up the elements of water, and so to become sugar. 

This process takes place commonly in the leaves where starch is formed, 
but especially in seeds, tubers (during the sprouting, etc.), and other parts 
which tlje plant uses as storehouses for starch food. It is probable that 
the same conditions of temperature and moisture which favor germination 
or active growth are also favorable to the production of diastase. 
1/ 160. Experiments to show the action of diastase. — (a) Place a bit of 
* starch half as large as a pea in a test tube, and cover with a weak solution * 
(about \ per cent) of commercial taka diastase. After it has stood in a 
warm place for five or ten minutes test with Fehling's solution. The pre- 
cipitate of cuprous oxide appears showing that some of the starch has been 
changed to sugar. By using measured quantities, and by testing with 
iodine at frequent intervals, it can be determined just how long it takes a 
given quantity of diastase to change a known quantity of starch. In this 
connection one should first test a portion of the same starch with Fehling's 
solution to show that no sugar is present. 

(b) Repeat the above experiment using a little tissue from a potato, and 
some from a corn seed. 

(c) Take 25 germinating barley seeds in which the radicle is just appear- 
ing. Grind up thoroughly in a mortar with about three parts of water. 
After this has stood for ten or fifteen minutes, filter. Fill a test tube one- 
third full of water, add a piece of starch half the size of a pea or less, and 
boil the mixture to make starch-paste. Add the barley extract. Put in a 
warm place and test from time to time with iodine. The first samples so 
treated will be blue, later ones violet, brown, and finally colorless, showing 



* This solution of taka diastase should be made up cold. If it is heated 
to 6o° C. or over it is destroyed. 



7% PHYSIOLOGY. 

that the starch has all disappeared. This is due to the action of the dias- 
tase which was present in the germinating seeds, and which was dissolved 
out and added to the starch mixture. The office of this diastase is to 
change the starch in the seeds to sugar. Germinating wheat is sweet, and 
it is a matter of common observation that bread made from sprouted wheat 
is sweet. 

(d) Put a little starch-paste in a test tube and cover it with saliva from 
the mouth. After ten or fifteen minutes test with Fehling's solution. A 
strong reaction appears showing how quickly and effectively saliva acts in 
converting starch to sugar. Successive tests with iodine will show the 
gradual disappearance of the starch. 

161. These experiments have shown us that diastase from three different 
sources can act upon starch converting it into sugar. The active principle 
in the saliva is an animal diastase (ptyalin), which is necessary as one step 
in the digestion of starch food in animals. The taha diastase is derived 
from a fungus (Eurotium oryzag) which feeds on the starch in rice grains 
converting it into sugar which the fungus absorbs for food. The malt dias- 
tase and leaf diastase are formed by the seed plants. That in seeds con- 
verts the starch to sugar which is absorbed by the embryo for food. That 
in the leaf converts the starch into sugar so that it can. be transported to 
other parts of the plant to be used in building new tissue, or to be stored 
again in the form of starch (example, the potato, in seeds, etc.). The 
starch is formed in the leaf during the daylight. The light renders the 
leaf diastase inactive. But at night the leaf diastase becomes active and 
converts the starch made during the day. Starch is not soluble in water, 
while the sugar is, and the sugar in solution is thus easily transported 
throughout the plant. In those green plants which do not form starch in 
their leaves (sugar beet, corn, and many monocotyledons), grape sugar 
and fruit sugar are formed in the green parts as the result of photosynthesis. 
In some, like the corn, the grape sugar formed in the leaves is transported 
to other parts of the plant, and some of it is stored up in the seed as starch. 
In others like the sugar beet the glucose and fruit sugar formed in the 
feaves flow to other parts of the plant, and much of it is stored up as cane 
sugar in the beet root. The process of photosynthesis probably proceeds 
in the same way in all cases up to the formation of the grape sugar and 
fruit sugar in the leaves. In the beet, corn, etc., the process stops here, 
while in the bean, clover, and most dicotyledons the process is carried one- 
step farther in the leaf and starch is formed. 



ANALYSIS OF PLANT SUBSTANCE. 79 



3. Rough Analysis of Plant Substance. 

162. Some simple experiments to indicate the nature of plant substance. — 

After these building-up processes of the plant, it is instructive to perform 
some simple experiments which indicate roughly the nature of the plant 
substance, and serve to show how it can be separated into other substances, 
some of them being reduced to the form in which they existed when the 
plant took them as food. For exact experiments and results it would be 
necessary to make chemical analyses. 

163. The water in the plant. — Take fresh leaves o 1 " leafy shoots or other 
fresh plant parts. Weigh. Permit them to remain in a dry room until 
they are what we call "dry." Now weigh. The plants have lost weight, 
and from what we have learned in studies of transpiration this loss in weight 
we know to result from the loss of water from the plant. 

164. The dry plant material contains water. — Take air-dry leaves, shav- 
ings, or other dry parts of plants. Place them in a test tube. With a 
holder rest the tube in a nearly horizontal position, with the bottom of the 
tube in the flame of a Bunsen burner. Very soon, before the plant parts 
begin to "burn," note that moisture is accumulating on the inner surface 
of the test tube. This is water driven off which could not escape by drying 
in air, without the addition of artificial heat, and is called "hygroscopic 
water." 

165. Water formed on burning the dry plant material. — Light a soft-pine 
or bass-wood splinter. Hold a thistle tube in one hand with the bulb down- 
ward and above the flame of the splinter. Carbon will be deposited over 
the inner surface of the bulb. After a time hold the tube toward the win- 
dow and look through it above the carbon. Drops of water have accumu- 
lated on the inside of the tube. This water is formed by the rearrangement 
of some of the hydrogen and oxygen, which is set free by the burning of 
the plant material, where they were combined with carbon, as in the cellu- 
lose, and with other elements. 

166. Formation of charcoal by burning.— Take dried leaves, and shav- 
ings from some soft wood. Place in a porcelain crucible, and cover about 
3 cm. deep with dry fine earth. Place the crucible in the flame of a Bun- 
sen burner and let it remain for about fifteen minutes. Remove and empty 
the contents. If the flame was hot the plant material will be reduced to a 
good quality of charcoal. The charcoal consists largely of carbon. 

167. The ash of the plant. — Place in the porcelain crucible dried leaves 
and shavings as before. Do not cover with earth. Place the crucible in 
the flame of the Bunsen burner, and for a moment place on the porcelain 
cover; then remove the cover, and note the moisture on the under surface 
from the escaping water. Permit the plant material to burn; it may even 
flame for a time. In the course of fifteen minutes it is reduced to a whitish 



8o 



PHYSIOLOG V. 



powder, much smaller in bulk than the charcoal in the former experiment. 
This is the ash of the plant. 

168. What has become of the carbon ? — In this experiment the air was 
not excluded from the plant material, so that oxygen combined with carbon 
as the water was freed, and formed carbon dioxide, passing off into the air 
in this form. This it will be remembered is the form in which the plant 
took the carbon-food in through the leaves. Here the carbon dioxide met 
the water coming from the soil, and the two united to form, ultimately, 
starch, cellulose, and other compounds of carbon; while with the addition 
of nitrogen, sulphur, etc., coming also from the soil, still other plant sub- 
stances were formed. 

169. The carbohydrates are classed among the non-nitrogenous sub- 
stances. Other non-nitrogenous plant substances are the organic acids 
like oxalic acid (H 2 C 2 4 ), malic acid (H 2 C 4 H 4 O a ), etc.; the fats and fixed 
oils, which occur in the seeds and fruits of many plants. Of the nitrogenous 
substances the proteids have a very complex chemical formula and contain 
carbon, hydrogen, oxygen, nitrogen, sulphur, etc. (example, aleuron, or 
proteid grains, found in seeds). The proteids are the source of nitrogenous 
food for the seedling during germination. Of the amides, asparagin 
(C,H 8 N,0 3 ) is an example of a nitrogenous substance; and of the alkaloids, 
nicotin (C ;0 H 14 N 2 ) from tobacco. 

All living plants contain a large per cent of water. According to Vines 
"ripe seeds dried in the air contain 12 to 15 per cent of water, herbaceous 
plants 60 to 80 per cent, and many water-plants and fungi as much as 95 
per cent of their weight." When heated to ioo° C. the water is driven off. 
The dry matter remaining is made up partly of organic compounds, exam- 
ples of which are given above, and inorganic compounds. By burning this 
dry residue the organic substances are mostly changed into volatile prod- 
ucts, principally carbonic acid, w T ater, and nitrogen. The inorganic sub- 
stances as a result of combustion remain as a white or gray powder, the ash. 

The amount of the ash increases with the age of the plant, though the 
percentage of ash may vary at different times in the different members of 
the plant. The following table taken from Vines will give an idea of the 
amount and composition of the ash in the dry solid of a few plants: 
CONTENT OF 1000 PARTS OF DRY SOLID MATTER. 





< 


in 
oS 

O 
0. 


OS 


B 
13 


id 

& 3 


O 


o-2 

O O 



to 


CO 


.5 

'u 

O 


Clover, in blossom 

Wheat, grain 

Wneat, straw. . . . 
Potato tubers. . . . 

Apples 

Peas (the seed). . . 


68.3 

19.7 

53-7 
37-7 
14.4 
27-3 


21 . 96 

6. 14 
7-33 

22 . 76 
5-14 

11. 41 


1 -39 

0.44 
0.74 
0.99 
3-76 
. 26 


24. 06 
0.66 
3.09 
0.97 
0.59 
1.36 


7-44 
2.36 
1 -33 
1.77 
1 . 26 
2.17 


0.72 
. 26 
0.33 
o.4S 
0. 20 
0. 16 


6.74 

9. 26 

2.58 
6.53 

1 .96 
9-95 


2 . 06 

.07 

1.32 
2.4s 
0.88 
0,95 


1 . 62 

0.42 

36.25 

0.80 
. 62 
0. 24 


2.66 

0.04 
. 90 
1. 17 

0.42 



CHAPTER IX. 

HOW PLANTS OBTAIN THEIR FOOD. I. 

1. Sources of Plant Food. 

170. The necessary constituents of plant food. — As indicated in Chap- 
ter 3, investigation has taught us the principal constituents of plant food. 
Some suggestion as to the food substances is derived by a chemical analysis 
of various plants. In Chapter 8 it was noted that there are two principal 
kinds of compounds in plant substances, the organic compounds and the 
inorganic compounds or mineral substances. The principal elements in 
the organic compounds are hydrogen, carbon, oxygen and nitrogen. The 
elements in the inorganic compounds which have been found indispensable 
to plant growth are calcium* potassium, magnesium, phosphorus, sulphur 
and iron. (See paragraphs 54-58, and complete observations on water 
cultures.) Other elements are found in the ash of plants; and while they 
are not absolutely necessary for growth, some f of them are beneficial in 
one way or another. 

171. The carbohydrates are derived, as we have learned, from the CC) 2 
of the air, and water in the plant tissue drawn from the soil; though in the 
case of aquatic plants entirely submerged, all the constituents are absorbed 
from the surrounding water. 

172. Food substances in the soil. — Land plants derive their mineral food 
from the soil, the soil received the mineral substances from dissolving and 
disintegrating rocks. Nitrogenous food is chiefly derived from the same 
source, but under a variety of conditions which will be discussed in later 
paragraphs, but the nitrogen comes primarily from the air. Some of the 
mineral substances, those which are soluble as well as some of the nitrog- 
enous substances, are found in solution in the soil. These are absorbed 
by the plant, as needed, along with water, through the root hairs. 



* Calcium is not essential for the growth of the fungi, 
f For example, silicon is used by some plants in strengthening supporting 
tissues. Buckwheat thrives better when supplied with a chloride. 

81 



82 PHYSIOLOGY. 

173. Absorption of soluble substances. — Since these substances are dis- 
solved in the water of the soil, it is not necessary for us to dwell on the 
process of absorption. This in general is dwelt upon in Chapter 3. It 
should be noted, however, that food substances in solution, during absorp- 
tion, diffuse through the protoplasmic membrane independently of each 
other and also independently of the rate of movement of the water from 
the soil into the root hairs and cells of the root. 

When the cells have absorbed a certain amount of a given substance, no 
more is absorbed until the concentration of the cell-sap in that particular 
substance is reduced. This, however, does not interfere with the absorp- 
tion of water, or of other substances in solution by the same cells. Plants 
have therefore a certain selective power in the absorption of food substances. 

174. Action of root hairs on insoluble substances. Acidity of 
root hairs. — If we take a seedling which has been grown in a 
germinator, or in the folds of cloths or paper, so that the roots are 
free from the soil, and touch the moist root hairs to blue litmus 
paper, the paper becomes red in color where the root hairs have 
come in contact. This is the reaction for the presence of an acid 
salt, and indicates that the root hairs excrete certain acid sub- 
stances. This acid property of the root hairs serves a very im- 
portant function in the preparation of certain of the elements of 
plant food in the soil. Certain of the chemical compounds of 
potash, phosphoric acid, etc., become deposited on the soil par- 
ticles, and are not soluble in water. The acid of the root hairs 
dissolves some of these compounds where the particles of soil are 
in close contact with them, and the solutions can then be taken up 
by the roots. Carbonic acid and other acids are also formed in 
the soil, and aid in bringing these substances into solution. 

175. This corrosive action of the roots can be shown by the well-known 
experiment of growing a plant on a marble plate which is covered by soil 
In lieu of the marble plate, the peas may be planted .in clam or oyster 
shells, which are then buried in the soil of the pot, so that the roots of the 
seedlings will come in contact with the smooth surface of the shell. After 
a few weeks, if the soil be washed from the marble where the roots have 
been in close contact, there will be an outline of this part of the root sys- 
tem. Several different acid substances are excreted from the roots of 
plants which have been found to redden blue litmus paper by contact 
Experiments by Czapek show, however, that the carbonic acid excreted by 
the roots has the power of directly bringing about these corrosion phenom- 



PARASITES AND SAPROPHYTES. 83 

ena. The acid salts are the substances which are most actively concerned 
in reddening the blue litmus paper. They do not directly aid in the corro- 
sion phenomena. In the soil, however, where these compounds of potash, 
phosphoric acid, etc., are which are not soluble in water, the acid salt 
(primary acid potassium phosphate) which is most actively concerned in 
reddening the blue litmus paper may act indirectly on these mineral sub- 
stances, making them available for plant food. This salt soon unites with 
certain chlorides in the soil, making among other things small quantities 
of hydrochloric acid. 

176. Note. — It is a general rule that plants cannot take solid food into 
their bodies, but obtain all food in either a liquid or gaseous state. The 
only exception to this is in the case of the plasmodia of certain Myxomy- 
cetes (Slime Moulds), and also perhaps some of the Flagellates and other 
very low forms, which engulf solid particles of food. It is uncertain, how- 
ever, whether these organisms belong to the plant or animal kingdom, 
and they probably occupy a more or less intermediate position. 

177. Action of nitrite and nitrate bacteria. — Many of the higher green 
plants prefer their nitrogenous food in the form of nitrates. (Example, 
nitrate of soda, potassium nitrate, saltpetre.) Nitrates are constantly 

>eing formed in soil by the action of certain bacteria. The nitrite bacteria 
(Nitromonas) convert ammonia in the soil to nitrous acid (a nitrite), while 
at this point the nitrate bacteria (Nitrobacter) convert the nitrites into 
nitrates. The fact that this nitrification is going on constantly in soil is of 
the utmost importance, for while commercial nitrates are often applied 
to the soil, the nitrates are easily washed from the soil by heavy rains. 
These nitrite and nitrate bacteria require oxygen for their activity, and 
they are able to obtain their carbohydrates by decomposing organic matter 
in the soil, or directly by assimilating the CO, in the soil, deriving the energy 
for the assimilation of the carbon dioxide from the chemical process of 
nitrification. This kind of carbon dioxide assimilation is called chemo- 
synthetic assimilation. 

l^~ 2. Parasites and Saprophytes. 

178. Parasites among the fungi. — A parasite is an organism which 
derives all or a part of its food directly from another living organism (its 
host) and at the latter's expense. The larger number of plant parasites 
are found among the fungi (rusts, smuts, mildews, etc.). (See Nutrition of 
the Fungi, paragraph 185.) Some of these are not capable of develop- 
ment unless upon their host, and are called obligate parasites. Others can 
grow not only as parasites but at other times can also grow on dead organic 
matter, and are called facultative parasites, i.e. they can choose either a 
parasitic life or a saprophytic one. 

179. Parasites among the seed 'plants. — Cuscuta. — There are, however, 
parasites among the seed plants; for example, the dodder (Cuscuta), para- 



84 



PHYSIOLOGY. 



sitic on clover, and a great variety of other plants. There is food enough 
in the seed for the young plant to take root and develop a slender stem until 
it takes hold of its host. It then twines around the stem of its host send- 
ing wedge-shaped haustoria into the stem to obtain food. The part then 
in connection with the ground dies. 

The haustoria of the dodder form a complete junction with the vascular 
bundles of its host so that through the vessels water and salts are obtained, 
while through the junction of sieve tubes the elaborated organic food is 




obtained. The union of the dodder with its host is like that between a 
graft and the graft stock. The beech drops (Epiphegus) is another exam- 
ple of a parasitic seed plant. It is parasitic on the roots of the beech. 

180. The mistletoe (Viscum album), which grows on the branches of 
trees, sends its roots into the branches, and only the vessels of the vascular 
system are fused according to some. If this is true then it probably ob- 
tains only water and salts from its host. But the mistletoe has green leaves 
and is thus able to assimilate carbon dioxide and manufacture its own 



PARASITES AND SAPROPHYTES. 85 

organic substances. It is claimed by some, however, that the host derives 
some food from the parasite during the winter when the host has shed its 
leaves, and if this is true it would seem that organic food could also be 
derived during the summer from the host by the mistletoe. 

181. Saprophytes. — A saprophyte is a plant which is enabled to obtain 
its food, especially its organic food, directly from dead animals or plants or 
from dead organic substances. Many fungi are saprophytes, as the moulds, 
mushrooms, etc. (See Nutrition of the Fungi.) 

182. Humus saprophytes. — The action of fungi as described in the pre- 
ceding chapter, as well as of certain bacteria, gradually converts the dead 
plants or plant parts into the finely powdered brown substance known as 
humus. In general the green plants cannot absorb organic food from 
humus directly. But plants which are devoid of chlorophyll can live 
saprophytically on this humus. They are known as humus saprophytes. 
Many of the mushrooms and other fungi, as well as some seed plants which 
lack chlorophyll or possess only a small quantity, are able to absorb all 
their organic food from humus. It is uncertain whether any seed plants 
can obtain all of their organic food directly from humus, though it is be- 
lieved that many can so obtain a portion of it. But a number of seed 
plants, like the Indian pipe (Monotropa) and certain orchids, obtain organic 
food from humus. These plants lack chlorophyll and cannot therefore 
manufacture their own carbohydrate food. Not being parasitic on plants 
which can, as in the case of the dodder and beech drops mentioned above, 
they undoubtedly derive their organic food from the humus. But fungus 
mycelium growing in the humus is attached to their roots, and in some 
orchids enters the roots and forms a nutritive connection. The fungus 
mycelium can absorb organic food from the humus and in some cases at 
least can transfer it over to the roots of the higher plant (see Mycorhiza). 

183. Autotrophic, heterotrophic, and mixotrophic plants. — An auto- 
trophic plant is one which is self-nourishing, i.e. it is provided with an 
abundant chlorophyll apparatus for carbon dioxide assimilation and with 
absorbing organs for obtaining water and salts. Heterotrophic plants 
are not provided with a chlorophyll apparatus sufficient to assimilate all 
the carbon dioxide necessary, so they nourish themselves by other means. 
Mixotrophic plants are those which are intermediate between the other two, 
i.e. they have some chlorophyll but not enough to provide all the organic 
food necessary, so they obtain a portion of it by other means. Evidently 
there are all gradations of mixotrophic plants between the two other kinds 
(example, the mistletoe). 

184. Symbiosis. — Symbiosis means a living with or living together, and 
is said of those organisms which live so closely in connection with each 
other as to be influenced for better or worse, especially from a nutrition 
standpoint. Conjunctive symbiosis has reference to those cases where 



S6 



PHYSIOLOGY. 



there Is a direct interchange of food material between the two organisms 
(lichens, mycorhiza, etc.) Disjunctive symbiosis has reference to an inter 
life relation without any fixed union between them (example, the relations 
between flowers and insects, ants and plants, and even in a broad sense the 
relation between saprophytic plants in reducing organic matter to a con- 
dition in which it may be used for food by the green plants, and these in 
turn provide organic matter for the saprophytes to feed upon, etc.). Antag- 
onistic symbiosis is shown in the relation of parasite to its host, reciprocal 
symbiosis, or mianalistic symbiosis is shown in those cases where both 
symbionts derive food as a result of the union (lichens, mycorhiza, etc.). 

3. How Fungi Obtain their Food. 
185. Nutrition of moulds. — In our study of mucor, as we have seen, the 

growing or vegetative part 
of the plant, the mycelium, 
lies within the substratum, 
which contains the food 
materials in solution, and the 
slender threads are thus 
bathed on all sides by them. 
The mycelium absorbs the 
watery solutions throughout 
the entire system of ramifica- 
tions. When the upright 
fruiting threads are devel- 
oped they derive the materials 
for their growth directly from 
the mycelium with which 
they are in connection. The 
moulds which grow on de- 
caying fruit or on other 
organic matter derive their 
nutrient materials in the same 
way. The portion of the 
mould which we usually see 
on the surface of these sub- 
stances is in general the fruit- 
ing part. The larger part 
of the mycelium lies hidden 
within the subtratum. 

186. Nutrition of para- 
sitic fungi. — Certain of the 
fungi grow on or within the 
higher plants and derive their food materials from, them and at their ex- 
pense. Such a fungus is called a parasite, and there are a large number 




Fig. 75- 
Carnation rust on leaf and flower stem, 
graph. 



From photo- 



HOW PLANTS OBTAIN FOOD. 



87 



of these plants which are known as parasitic fungi. The plant at whose 
expense they grow is called the "host." 

One of these parasitic fungi, which it is quite easy to obtain in green- 
houses or conservatories during the autumn and winter, is the carnation 
rust \Uromyces caryophyllinus), since it breaks out in rusty dark brown 
patches on the leaves and stems of the carnation (see fig. 75). If we make 
thin cross sections through one of these spots on a leaf, and place them for a 




Fig. 76. 
Several teleutospores, showing the variations in form. 

few minutes in a solution of chloral hydrate, portions of the tissues of the 
leaf will be dissolved. After a few minutes we wash the sections in water on 
a glass slip, and stain them with a solution of eosin. If the sections were care- 




Fig. 77. 
Cells from the stem of a rusted carnation, showing the intercellular mycelium and haustoria. 
Object magnified 30 times more than the scale. 

fully made, and thin, the threads of the mycelium will be seen coursing be- 
tween the cells of the leaf as slender threads. Here and there will be seen 
short branches of these threads which penetrate the cell wall of the host and 
project into the interior of the cell in the form of an irregular knob. Such 
a branch is a haustorium. By means of this haustorium, which is here 



88 



PHYSIOLOG Y. 



only a short branch of the mycelium, nutritive substances are taken by the 
fungus from the protoplasm or cell-sap of the carnation. From here it 
passes to the threads of the mycelium. These in turn supply food material 
for the development of the dark brown gonidia, which we see form the dark- 
looking powder on the spots. Many other fungi form haustoria, which take 
up nutrient matters in the way described for the carnation rust. In the case 

A 




Fig. 78. 
Cell from carnation leaf, showing 
haustorium of rust mycelium grasping 
the nucleus of the host. A, haustori- 
um ; n, nucleus of host. 



Fig. 7§- 
Intercellular mycelium with haustoria entering 
the cells. A , of Cystopus candidus (white rust) ; 
B, of Peronospora calotheca. (De Bary.) 



of other parasitic fungi the threads of the mycelium themselves penetrate 
the cells of the host, while in still others the mycelium courses only between 
the cells of the host (fungus of peach leaf-curl for example) and derives food 
materials from the protoplasm or cell-sap of the host by the process of 
osmosis. 

187. Nutrition of the larger fungi. — If we select some one 
of the larger fungi, the majority of which belong to the mush- 
room family and its relatives, which is growing on a decaying log 
or in the soil, we shall see on tearing open the log, or on remov- 
ing the bark or part of the soil, as the case may be, that the 
stem of the plant, if it have one, is connected with whitish 
strands. During the spring, summer, or autumn months, exam- 
ples of the mushrooms connected with these strands may usually 
be found readily in the fields or woods, but during the winter and 



HOW PLANTS OBTAIN FOOD, 



8 9 



colder parts of the year often they may be seen in forcing houses, 
especially those cellars devoted to the propagation of the mush- 
room of commerce. 

188. These strands are made up of numerous threads of the 
mycelium which are closely twisted and interwoven into a cord 
or strand, which is called a mycelium strand, or rhizomorph. 
These are well shown in fig. 236, which is from a photograph of 
the mycelium strands, or ' ' spawn ' ' as the grower of mushrooms 
calls it, of Agaricus campestris. The little knobs or enlargements 
on the strands are the young fruit bodies, or ' ' buttons. ' ' 

189. While these threads or strands of the mycelium in the 
decaying wood or in the decaying organic matter of the soil are 




Fig. 80. 

Sterile mycelium on wood props in coal mine, 400 feet below surface. (Photographed by 
the author.) 



90 PHYSIO LOG Y. 

not true roots, they function as roots, or root hairs, in the ab- 
sorption of food materials. In old cellars and on damp soil in 
moist places we sometimes see fine examples of this vegetative 
part of the fungi, the mycelium. But most magnificent examples 
are to be seen in abandoned mines where timber has been taken 
down into the tunnels far below the surface of the ground to 
support the rock roof above the mining operations. I have 
visited some of the coal mines at Wilkesbarre, Pa. , and here on 
the wood props and doors, several hundred feet below the surface, 
and in blackest darkness, in an atmosphere almost completely 
saturated at all times, the mycelium of some of the wood-destroy- 
ing fungi grows in a profusion and magnificence which is almost 
beyond belief. Fig. 80 is from a flash-light photograph of a 
beautiful example 400 feet below the surface of the ground. 
This was growing over the surface of a wood prop or post, and 
the picture is much reduced. On the doors in the mine one can 
see the strands of the mycelium which radiate in fan-like figures 
at certain places near the margin of growth, and farther back the 
delicate tassels of mycelium which hang down in fantastic figures, 
all in spotless white and rivalling the most beautiful fabric in the 
exquisiteness of its construction. 



^ 



190. How fungi derive carbohydrate food. — The fungi being devoid of 
chlorophyll cannot assimilate the C0 2 from the air. They are therefore 
dependent on the green plants for their carbohydrate food. Among the 
saprophytes, the leaf and wood destroying fungi excrete certain substances 
(known as enzymes) which dissolve the carbohydrates and certain other 
organic compounds in the woody or leafy substratum in which they grow. 
They thus produce a sort of extracellular digestion of carbohydrates, con- 
verting them into a soluble form which can be absorbed by the mycelium. 
The parasitic fungi also obtain their carbohydrates and other organic food 
from the host. The mycelium of certain parasitic, and of wood destroying 
fungi, excretes enzymes (cytase) which dissolve minute perforations in the 
cell walls of the host and thus aid the hypha during its boring action in 
penetrating cell walls. 

Note. — Certain wood destroying fungi growing in oaks absorb tannin 
directly, i.e. in an unchanged form. One of the pine destroying fungi 
(Trametes pint) absorbs the xylogen from the wood cells, leaving the pure 
cellulose in which the xylogen was filtrated; while Polyporus mollis absorbs 
the cellulose, leaving behind only the wood element. 



HOW PLANTS OBTAIN FOOD. 9 1 

4. Mycorhiza. 

191. While such plants as the Indian pipe (Monotropa), some of the 
orchids, etc., are humus saprophytes and some of them are possibly able to 
absorb organic food from the humus, many of them have fungus mycelium 
in close connection with their roots", and these fungus threads aid in the 
absorption of organic food. The roots of plants which have fungus myce- 
lium intimately associated in connection with the process of nutrition, are 
termed mycorhiza. There is a mutual interchange of food between the 
fungus and the host, a reciprocal symbiosis. 

192. Mycorhiza are of two kinds as regards the relation of the fungus to 
the root; ectolrophic (or epiphytic), where the mycelium is chiefly on the 
outside of the root, and endotrophic (or endophytic) where the mycelium is 
chiefly within the tissue of the root. 

193. Ectotrophic mycorhiza. — Ectotrophic mycorhiza occur on the roots 
of the oak, beech, hornbean, etc., in forests where there is a great deal of 
humus from decaying leaves and other vegetation. The young growing 
roots of these trees become closely covered with a thick felt of the mycelium, 
so that no root hairs can develop. The terminal roots also branch pro- 
fusely and are considerably thickened. The fungus serves here as the 
absorbent organ for the tree. It also acts on the humus, converting some 
of it into available plant food and transferring it over to the tree. 

194. Endotrophic mycorhiza. — These are found on many of the humus 
saprophytes, which are devoid of chlorophyll, as well as on those possess- 
ing little or even on some plants possessing an abundance, of chlorophyll. 
Examples are found in many orchids (see the coral root orchid, for exam- 
ple), some of the ferns (Botrychium), the pines, leguminous plants, etc. 
In endotrophic mycorhiza the mycelium is more abundant within the tissues 
of the root, though some of the threads extend to the outside. In the case 
of the mycorhiza on the humus saprophytes which have no chlorophyll, or 
but little, it is thought by some that the fungus mycelium in the humus 
assists in converting organic substances and carbohydrates into a form 
available for food by the higher plant and then conducts it into the root, 
thus aiding also in the process of absorption, since there are few or no root 
hairs on the short and fleshy mycorhiza. The roots, however, of some of 
these humus saprophytes have the power of absorbing a portion of their 
organic compounds from the humus. It is thought by some, though not 
definitely demonstrated, that in the case of the oaks, beeches, hornbeans, 
and other chlorophyll-bearing symbionts, the fungus threads do not absorb 
any carbohydrates for the higher symbiont, but that they actually derive 
their carbohydrates from it.* But it is reasonably certain that the fungus 



* Evidence points to the belief that certain cells of the host form sub- 
stances which attract, chemitropicallv, the fungus threads, and that in 
these cells the fungus threads are more abundant than in others. Further- 



9 2 



PHYSIOLOGY. 



threads do assimilate from the humus certain unoxidized, or feebly oxi- 
dized, nitrogenous substances (ammonia, for example), and transfer them 
over to the host, for the higher plants with difficulty absorb these sub- 
stances, while they readily absorb nitrates which are not abundant in 
humus. This is especially important in the forest. It is likely therefore 

5. Nitrogen gatherers. 
195. How clovers, peas, and other legumes gather nitrogen. — It has long 
been known that clover plants, peas, beans, and 
many other leguminous plants are often able to 
thrive in soil where the cereals do but poorly. 
Soil poor in nitrogenous plant food becomes richer 
in this substance where clovers, peas, etc., are 
grown, and they are often planted for the purpose 
of enriching the soil. Leguminous plants, espe- 
cially in poor soil, are almost certain to have en- 
largements, in the form of nodules, or "root 
tubercles." A root of the common vetch with 
some of these root tubercles is shown in fig. 8i. 

196. A fungal or bacterial organism in these 
root tubercles. — If we cut one of these root tuber- 
cles open, and mount a small portion of the in- 
terior in water for examination with the micro- 
scope, we shall find small rod-shaped bodies, 
some of which resemble bacteria, while others are more or less forked into 
forms like the letter Y, as shown in fig. 82. These bodies are rich in 
nitrogenous substances, or proteids. They are portions of a minute organism, 
of a fungus or bacterial nature, which attacks the roots of leguminous plants 




Fig. 81. 
Root of the common vetch, 
showing root tubercles. 




efcto^ 



Fig. 82. Fig. 83. 

Root-tubercle organism from vetch, old con- Root-tubercle organism from Medicago 
dition. - denticulata. 

and causes these nodular outgrowths. The organism (Phytomyxa legumi- 
nosarum) exists in the soil and is widely distributed where legumes grow. 

more in the vicinity of the nucleus of the host seems to be the place where 
these activities are more marked. 



HOW PLANTS OBTAIN FOOD. 93 

197. How the organism gets into the roots of the legumes. — This minute 
organism in the soil makes its way through the wall of a root hair near the 
end. It then grows down the interior of the root hair in the form of a 
thread. When it reaches the cell walls it makes a minute perforation, 
through which it grows to enter the adjacent cell, when it enlarges again. 
In this way it passes from the root hair to the cells of the root and down to 
near the center of the root. As soon as it begins to enter the cells of the 
root it stimulates the cells of that portion to greater activity. So the root 
here develops a large lateral nodule, or "root tubercle." As this "root 
tubercle" increases in size, the fungus threads branch in all directions, 
entering many cells. The threads are very irregular in form, and from cer- 
tain enlargements it appears that the rod-like bodies are formed, or the 
thread later breaks into myriads of these small " bacteroids. " 

198. The root organism assimilates free nitrogen for its host. — This 
organism assimilates the free nitrogen from the air in the soil, to make the 
proteid substance which is found stored in the bacteroids in large quantities. 
Some of the bacteroids, rich in proteids, are dissolved, and the proteid sub- 
stance is made use of by the clover or pea, as the case may be. This is why 
such plants can thrive in soil with a poor nitrogen content. Later in the 
season some of the root tubercles die and decay. In this way some of the 
proteid substance is set free in the soil. The soil thus becomes richer in 
nitrogenous plant food. 

The forms of the bacteroids vary. In some of the clovers they are oval, 
in vetch they are rod-like or forked, and other forms occur in some of the 
other genera. 

199. Note. — So far as we know the legume tubercle organism does not 
assimilate free nitrogen of the air unless it is within the root of the legume. 
But there are microorganisms in the soil which are capable of assimilating 
free nitrogen independently. Example, a bacterium, Clostridium pasteur- 
ianum. Certain bacteria and algae live in contact symbiosis in the soil, the 
bacteria fixing free nitrogen, while in return for the combined nitrogen, the 
algae furnish the bacteria with carbohydrates. It seems that these bac- 
teria cannot fix the free nitrogen of the air unless they are supplied with 
carbohydrates, and it is known that Clostridium pasteurianum cannot assim- 
ilate free nitrogen unless sugar is present. 

6. Lichens. 



200. Nutrition of lichens. — Lichens are* very curious plants which grow 
on rocks, on the trunks and branches of trees, and on the soil. They form 
leaf-like expansions more or less green in color, or brownish, or gray, or they 
occur in the form of threads, or small tree-like formations. Sometimes the 



94 PHYSIOLOG V. 

plant fits so closely to the rock on which it grows that it seems merely t<, 
paint the rock a slightly different color, and in the case of many which occur on 
trees there appears to be to the eye only a very slight discoloration of the bark 
of the trunk, with here and there the darker colored points where fruit bodies 




Fig. 
Frond of lichen (peltigera), showing rhizoids. 

are formed. The most curious thing about them is, however, that while they 
form plant bodies of various form, these bodies are of a "dual nature" as 
regards the organisms composing them. The plant bodies, in other words, are 
formed of two different organisms which, woven together, exist apparently 
as one. A fungus on the one hand grows around and encloses in the 
meshes of its mycelium the cells or threads of an alga, as the case may be. 

If we take one of the leaf-like forms known as peltigera, which grows on 
damp soil or on the surfaces of badly decayed logs, we see that the plant 
body is flattened, thin, crumpled, and irregularly lobed. The color is dull 
greenish on the upper side, while the under side is white or light gray, and 
mottled with brown, especially the older portions. Here and there on the 
under surface are quite long slender blackish strands. These are composed 
entirely of fungus threads and serve as organs of attachment or holdfasts, 
and for the purpose of supplying the plant body with mineral substances 
which are in solution in the water of the soil. If we make a thin section of 
the leaf-like portion of a lichen as shown in fig. 85, we shall see that it is 
composed of a mesh of colorless threads which in certain definite portions 
contain entangled green cells. 'The colorless threads are those of the fungus, 
while the green cells are those of the alga. These green cells of the alga per- 
form the function of chlorophyll bodies for the dual organism, while the threads 
of the fungus provide the mineral constituents of plant food. The alga, 



HO W PLANTS OBTAIN FOOD. 



95 



while it is not killed in the embrace of the fungus, does not reach the per- 
fect state of development which it attains when not in connection with the 
fungus. On the other hand the fungus profits more than the alga by this 
association. It forms fruit bodies, and perfects spores in the special fruit 
bodies, which are so very distinct in the case of so many of the species of 
the lichens. These plants have lived for so long a time in this close associa- 
tion that the fungi are rarely found separate from the algae in nature, but in 
a number of cases they have been induced to grow in artificial cultures sep- 




Fig. 8s. 
Lichen (peltigera), section of thallus ; dark zone of rounded bodies made up largely of the 
algal cells. Fungus cells above, and threads beneath and among the algal cells. 



irate from the alga. This fact, and also the fact that the algae are often 
found to occur separate from the fungus in nature, is regarded by many as an 
indication that the plant body of the lichens is composed of two distinct or- 
ganisms, and that the fungus is parasitic on the alga. 

201. Others regard the lichens as autonomous plants, that is, the two or- 
ganisms have by this long-continued community of existence become unified 
into an individualized organism, which possesses a habit and mode of life 



9 6 



PHYSIOLOGY 



distinct from that of either of the organisms forming the component parts. 
This community of existence between two different organisms is called by 
some mutualism, or symbiosis. While the alga inclosed within the meshes 
of the fungus is not so free to develop, and probably does not attain the full 
development which it would alone under favorable conditions, still it is 




Fig. 86. 

Section of fruit body or apothecium of lichen (parmelia), showing asci and spores 
of the fungus. 

very likely that it is often preserved from destruction during very dry 
periods, within the tough thallus, on the surface of bare rocks. 



CHAPTER X. 

HOW PLANTS OBTAIN THEIR FOOD, II. 
Seedlings. 

202. It is evident from some of the studies which we have made in con- 
nection with germination of seeds and nutrition of the plant that there is a 
period in the life of the seed plants in which they are able to grow if sup- 
plied with moisture, but may entirely lack any supply of food substance 
from the outside, though we understand that growth finally comes to a 
standstill unless they are supplied with food from the outside. In con- 
nection with the study of the nutrition of the plant, therefore, it will be well 
to study some of the representative seeds and seedlings to learn more accu- 
rately the method of germination and nutrition in seedlings during the ger- 
minating period. 

203. To prepare seeds for germination. — Soak a handful of seeds (or 
more if the class is large) in water for 12 to 24 hours. Take shallow crockery 
plates, or ordinary plates, or a germinator with a fluted bottom. Place in 
the bottom some sheets of paper, and if sphagnum moss is at hand scatter 
some over the paper. If the moss is not at hand, throw the upper layer of 
paper into numerous folds. Thoroughly wet the paper and moss, but do 
not have an excess of water. Scatter the seeds among the moss or the folds 
of the paper. Cover with some more wet paper and keep in a room where 
the temperature is about 20 C. to 25 C. The germinator should be looked 
after to see that the paper does not become dry. It may be necessary to 
cover it with another vessel to prevent the too rapid evaporation of the water. 
The germinator should be started about a week before the seedlings are 
wanted for study. Some of the soaked seeds should be planted in soil in 
pots and kept at the same temperature, for comparison with those grown in 
the germinator. 

204. Structure of the grain of corn. — Take grains of corn that have been 

97 



9^ PHYSIO LOG V. 

soaked in water for 24 hours and note the form and difference in the two 
sides (in all of these studies the form and structure of the seed, as well as 
the stages in germination, should be illustrated by the student). Make a 
longisection of a grain of corn through the middle line, if necessary 
making several in order to obtain one which shows the structures well near 
the smaller end of the grain. Note the following structures: 1st, the hard 

outer "wall" (formed of the consoli- 
dated wall of the ovary with the in- 
teguments of the ovules — see Chap- 
ters 35 and 36); 2d, the greater mass 

Section of com seed ''at upper right of of starch and other P lant food (the 
each is the plantlet, next the cotyledon, at endosperm) in the centre: 3d, a some- 
left the endosperm. , \ , 

what crescent-shaped body (the 

scutellum) lying next the endosperm and near the smaller end of the 
grain; 4th, the remaining portion of the young embryo lying between the 
scutellum and the seed coat in the depression. When good sections are 
made one can make out the radicle at the smaller end of the seed, and a 
few successive leaves (the plumule) which lie at the opposite end of the 
embryo shown by sharply cuived parallel lines. Observe the attachment 
of the scutellum to the caulicle at the point of junction of the plumule and 
the radicle. The scutellum is a part of the embryo and represents a coty- 
ledon. The endosperm is also called albumen, and such a seed is albumin- 
ous. 

Dissect out an embryo from another seed, and compare with that seen in 
the section. 

205. In the germination of the grain of corn the endosperm supplies the 
food for the growth of the embryo until the roots are well established in 
the soil and the leaves have become expanded and green, in which stage 
the plant has become able to obtain its food from the soil and air and live 
independently. The starch in the endosperm cannot of course be used for 
food by the embryo in the form of starch. It is first converted into a solu- 
ble form and then absorbed through the surface of the scutellum or coty- 
ledon and carried to all parts of the embryo. An enzyme developed by the 
embryo acts upon the starch, converting it into a form of sugar which is in 
solution and can thus be absorbed. This en2yme is one of the so-called 
diastatic " ferments " which are formed during the germination of all seeds 
which contain iood stored in the form of starch. In some seedlings, 
this diastase formed is developed in much greater abundance than in 
others, for example, in barley. Examine grains of corn still attached 
to seedlings several weeks old and note that a large part of their content 
has been used up. The action of diastase on starch is described in 
Chapter 8. 



HOW PLANTS OBTAIN THE IT FOOD. 



99 



206. Structure of the pumpkin seed. — The pumpkin seed has 
a tough papery outer covering for the protection of the embryo 
plant within. This covering is made up of the seed coats. 
When the seed is opened by slitting off these coats there is seen 
within the "meat" of the pumpkin seed. This is nothing 
more than the embryo plant. The larger part of this embryo 
consists of two flattened bodies which are more prominent than 
any other part of the plantlet at this time. These two flattened 
bodies are the two first leaves, usually called cotyledons. If we 
spread these cotyledons apart we see that they are connected at 
one end. Lying between them at this point of attachment is a 
small bud. This is the plumule. The plumule consists of the 
very young leaves at the end of the stem which will grow as the 
seed germinates. At the other end where the cotyledons are 
joined is a small projection, the young root, often termed the 
radicle. 

207. How the embryo gets out of a pumpkin seed.- — To see 
how the embryo gets out of the pumpkin seed we should 
examine seeds germinated in the folds of damp paper or on damp 
sphagnum, as well as some which have been germinated in earth. 
Seeds should be selected which represent several different stages 
of germination. 




Germinating- seed of pumpkin, showing how the heel or " peg " catches on the seed coat 
to cast it off. 

208. The peg helps to pull the seed coats apart. — The root 
pushes its way out from between the stout seed coats at the 
smaller end, and then turns downward unless prevented from so 



. 



too 



PHYSIOLOGY. 



doing by a hard surface. After the root is 2-^cm long, and the 
two halves of the seed coats have begun to be pried apart, if we 

look in this rift at the 
junction of the root 
and stem, we shall see 
that one end of the seed 
coat is caught against 
a heel, or ' ' p e g, ' ' 
which has grown out 
from the stem for this 
purpose. Now if we 
examine one which is 
a little 
more ad- 
vanced, 
we shall see this heel 
more distinctly, and 
also that the stem is 
arching out away from 
the seed coats. As the 
stem arches up its back 
in this way it pries with 
the cotyledons against 
the upper seed coat, 
but the lower seed coat 
is caught against this heel, and the two are pulled gradually 
apart. In this way the embryo plant pulls itself out from be- 
tween the seed coats. In the case of seeds which are planted 
deeply in the soil we do not see this contrivance unless we dig 
down into the earth. The stem of the seedling arches through 
the soil, pulling the cotyledons up at one end. Then it 
straightens up, the green cotyledons part, and open out their 
inner faces to the sunlight, as shown in fig. 90. If we dig into 
the soil we shall see that this same heel is formed on the stem, 
and that the seed coats are cast off into the soil. 




Fig. 89. 
Escape of the pumpkin seedling from the seed coat? 



HOW PLANTS OBTAIN THEIR FOOD. 101 

209. Parts of the pumpkin seedling. — During the germination 
of the seed all parts of the embryo have enlarged. This in- 
crease in size of a plant is one of the peculiarities of growth. 
The cotyledons have elongated and expanded somewhat, though 
not to such a great extent as the root and the stem. The 
cotyledons also have become green on exposure to the light. 
Very soon after the main root has emerged from the seed coats, 
other lateral roots begin to form, so that the 
root soon becomes very much branched. 
The main root with its branches makes 
up the root system of the seedling. Be- 
tween the expanded cotyledons is seen 
the plumule. This has enlarged some- 
what, but not nearly so much as the root, 
or the part of the stem which extends 
below the cotyledons. This part of the 
stem, i. e. , that 
part below the 
cotyledons and 
extending to the 
beginning of the 
root, is called in Fig. 9 o. 

., ... . Pumpkin seedling rising from the ground. 

all seedlings the 

hypocotyl, which means " below the cotyledon." 

210. The common garden bean. — The common garden bean 
or the lima bean, may be used for study. The garden bean it 
not so flattened or broadened as the lima bean. It is rounded- 
compressed, elongate slightly curved, slightly concave on one 
side and convex on the other, and the ends are rounded. At 
the middle of the concave side note the distinct scar (the hilum) 
formed where the bean seed separates from its attachment to 
the wall of the pod. Upon one side of this scar is a slight prom- 
inence which is continued for a short distance toward the end 
of the bean in the form of a slight ridge. This is the raphe, and 
represents that part of the stalk of the ovule which is joined to 
the side of the ovule when the latter is curved around against it 




102 



PHYSIOLOGY, 




(see Chapter 36), and at the outer end of the raphe is the cha- 
\aza> the point where the stalk is joined to the end of the ovule, 
best understood in a straight ovule. Upon the 
opposite side of the scar and close to it can be 
o-.-.-l m seen a minute depression, the micro pyle. Under- 
Q----M neath the seed coat and lying between this point 
fi ....Lr and the end of the seed is the embryo, which gives 
(k.../c greater prominence to the bean at this point, but it 
is especially more prominent after the bean has been 
soaked in water. Soak the beans in water and as 

Fig. 1 . 

Garden bean. tne y are swelling note how the seed coats swell 
^'hiium C o?sca?-, faster than the inner portion of the seed, which 
where e; cha£za causes them to wrinkle in a curious way, but finally 
the inner portion swells and fills the seed coat out 
smooth again. Sketch a bean showing all the external features 
both in side view and in front. Split one lengthwise and sketch 
the half to which the embryo clings, noting the young root, 
stem, and the small leaves which were lying 
between the cotyledons. There is no endo- 
sperm here now, since it was all used up in 
the growth of the embryo, and a large part of 
its substance was stored up in the cotyledons. 
As the seed germinates the young plant gets its 
first food from that stored in the cotyledons. Bean f eed sp 11 * 

J open to show plant- 

The hypocotyl elongates, becomes strongly St- 
arched, and at last straightens up, lifting the cotyledons from 
the soil. As the cotyledons become exposed to the light they 
assume a green color. Some of the stored food in them goes 
to nourish the embryo during germination, and they therefore 
become smaller, shrivel somewhat, and at last fall off. 

211. The castor- oil bean.— This is not a true bean, since it 
belongs to a very different family of plants (Euphorbiaceae). In 
the germination of this seed a very interesting comparison can 
be made with that of the garden bean. As the "bean" swells 
the very hard outer coat generally breaks open at the free end 
and slips off at the stem end. The next coat within, which is 




HO W PLANTS OBTAIN THEIR FOOD. 



I03 



also hard and shining black, splits open at the opposite end, that 
is at the stem end. It usually splits 
open in the form of three ribs. 
Next within the inner coat is a 
very thin, whitish film (the remains 
of the nucellus, and corresponding 
to the perisperm) which shrivels up 
and loosens from the white mass, 
the endosperm, within. In the 
castor-oil bean, then, the endosperm 
is not all absorbed by the embryo 
during the formation of the seed. 
As the plant becomes 
older we should note that 
the fleshy endosperm be- 
comes thinner and thin- 
ner, and at 
last 
nothing 



Fig. 93. 
How the garden bean comes out of the ground. First the looped hypocotyl, 
then the cotyledons pulled out, next casting off the seed coat, last the plant erect, 
bearing thick cotyledons, the expanding leaves, and the plumule between them. 

a thin, whitish film covering the green faces of the cotyledons. 
The endosperm has been gradually absorbed by the germinat- 
ing plant through its cotyledons and used for food. 




Arisaema triphyllum.* 

212. Germination of seeds of jack-in-the-pulpit. — The ovaries 

of jack-in-the-pulpit form large, bright red berries with a soft 

pulp enclosing one to several large seeds. The seeds are oval in 

form. Their germination is interesting, and illustrates one type 



* In lieu of Arisasma make a practical study of the pea. See paragraph 
216a. 



104 



PHYSIOLOG Y. 



of germination of seeds common among monocotyledonous plants. 
If the seeds are covered with sand, and 
kept in a moist place, they will germi- 
nate readily. 

213. How the embryo backs out of 
the seed. — The embryo lies within the 
mass of the endosperm; the root end, 
near the smaller end of the 
seed. The club-shaped 
cotyledon lies near the 





Fig. 94. 
Germination of castor-oil bean. 



middle of the seed, surrounded firmly on all sides by the endo- 
sperm. The stalk, or petiole, of the cotyledon, like the lower 
part of the petiole of the leaves, is a hollow cylinder, and 
contains the younger leaves, and the growing end of the stem 
or bud. When germination begins, the stalk, or petiole, of the 
cotyledon elongates. This pushes the root end of the embryo 
out at the small end of the seed. The free end of the embryo 
now enlarges somewhat, as seen in the figures, and becomes the 
bulb, or corm, of the young plant. At first no roots are visible,* 
but in a short time one, two, or more roots appear on the enlarged 
end. 

214. Section of an embryo.— If we make a longisection of 
the embryo and seed at this time we can see how the club- 
shaped cotyledon is closely surrounded by the endosperm. 
Through the cotyledon, then, the nourishment from the endo- 
sperm is readily passed over to the growing embryo. In the 
hollow part of the petiole near the bulb can be seen the first 
leaf. 



HOW PLANTS OBTAIN THEIR FOOD. 



105 




Fig- 95- 

Seedlings of castor-oil bean casting the seed coats, and showing papery remnant 
of the endosperm. 




Fig. 96. 
Seedlings of jack-in-the 
pulpit; embryo backing out 
uf the seed. 





Fig. 97- 
Section of germinating embryos 
of jack-in-the-pulpit, showing young 
leaves inside the petiole of the 
cotyledon. At the left cotyledon 
shown surrounded by the endo- 
sperm in the seed; at right endo- 
sperm removed to show the club- 
sfiaped cotyledon. 



io6 



PHYSIOLOG Y. 



215. How the first leaf appears. — As the embryo backs out 
of the seed, it turns downward into the soil, unless the seed 
is so lying that it pushes straight 
downward. On the upper side of 
arch thus formed, in the petiole 
the cotyledon, a slit appears, ; 
through this opening the first 
arches its way out. The loop of 
petiole comes out first, and the 
later, as shown in 
fig. 98. The petiole 
now gradually 





Fig. 98. Fig. 99. Fig. ico. 

Seedlings of jack-in -the- Embryos of jack-in-the-pulpit Seedling of jack-in- 

pulpit, first leaf arching still attached to the endosperm in the-pulpit; section 

out of the petiole of the seed coats, and showing the simple of the endosperm 

cotyledon. first leaf. and cotyledon. 

straightens up, and as it elongates the leaf expands. 

216. The first leaf of the jack-in-the-pulpit is a simple one. 
— The first leaf of the embryo jack-in-the-pulpit is very different 
in form from the leaves which we are accustomed to see on 
mature plants. If we did not know that it came from the seed 



HO W PLANTS OBTAIN THEIR FOOD. 107 

of this plant we would not recognize it. It is simple, that is it 
consists of one lamina or blade, and not of three leaflets as in 
the compound leaf of the mature plant. The simple leaf is 
ovate and with a broad heart-shaped base. The jack-in-the- 
pulpit, then, as trillium, and some other monocotyledonous 
plants which have compound leaves on the mature plants, have 
simple leaves during embryonic development. The ancestral 
monocotyledons are supposed to have had simple leaves. Thus 
there is in the embryonic development of the jack-in-the-pulpit, 
and others with compound leaves, a sort of recapitulation of the 
evolutionary history of the leaf in these forms. 

216a. Germination of the pea. — Compare with the bean. 
Note especially that the cotyledons are not lifted above the soil 
as in the beans. Compare germination of acorns. 

Digestion. 

2166. To test for stored food substance in the seedlings studied. — The 

pumpkin, squash, and castor-oil bean are examples of what are called oily 
seeds, since considerable oil is stored up in the protoplasm in the cotyle- 
dons. To test for this, remove a small portion of the substance from the 
cotyledon of the squash and crush it on a glass slip in a drop or two of 
osmic acid.* Put on a cover-glass and examine with a microscope. 
The black amorphous matter shows the presence of oil in the protoplasm. 
The small bodies which are stained yellow are aleurone grains, a form of 
protein or albuminous substance. Both the oil and the protein substance 
are used by the seedling during germination. The oil is converted into an 
available food form by the action of an enzyme called lipase, which splits 
up the fatty oil into glucose and other substances. Lipase has been found 
in the endosperm of the castor oil, cocoanut, and in the cotyledons of the 
pumpkin, as well as in other seeds containing oil as a stored product. The 
aleurone is made available by an enzyme of the nature of trypsin. Test 
the endosperm of the castor-oil bean in the same way. Make another test 
of both the squash and castor-oil seeds with iodine to show that starch is 
not present. 

Test the cotyledon of the bean with iodine for the presence of starch. If 
the endosperm of corn seed has not been tested do so now with iodine. 
The endosperm consists largely of starch. The starch is converted to glu- 



* Dissolve a half gram of osmic acid in 50 cc. of water and keep tightly 
corked when not using. 



IOS PHYSIOLOGY. 

cose by a diastatic " ferment " formed by the seedling as it germinates. 
Make a thin cross-section of a grain of wheat, including the seed coat and a 
portion of the interior, treat with iodine and mount for microscopic exam- 
ination. Note the abundance of starch in the internal portion of endo- 
sperm. Note a layer of cells on the outside of the starch portions filled 
with small bodies which stain yellow. These are aleurone grains. The 
cellulose in the cell walls of the endosperm is dissolved by another enzyme 
called cytase, and some plants store up cellulose for food. For example, in 
the endosperm of the date the cell walls are very much thickened and pitted. 
The cell walls consist of reserve cellulose and the seedling makes use of it 
for food during growth. 

216c. Albuminous and exalbuminous seeds. — In seeds where the food is 
stored outside of the embryo they are called albuminous; examples, corn, 
wheat and other cereals, Indian turnip, etc. In those seeds where the food 
is stored up in the embryo they are called exalbuminous; examples, bean, 
pea, pumpkin, squash, etc. 

217. Digestion has a well-defined meaning in animal physiology and 
relates to the conversion of solid food, usually within the stomach, into a 
soluble form by the action of certain gastric juices, so that the liquid food 
may be absorbed into the circulatory system. The term is not often ap- 
plied in plant physiology, since the method of obtaining food is in general 
fundamentally different in plants and animals. It is usually applied to 
the process of the conversion of starch into some form of sugar in solution, 
as glucose, etc. This we have found takes place in the leaf, especially at 
night, through the action of a diastatic ferment developed more abundantly 
in darkness. As a result, the starch formed during the day in the leaves is 
digested at night and converted into sugar, in which form it is transferred 
to the growing parts to be employed in the making of new tissues, or it is 
stored for future use; in other cases it unites with certain inorganic sub- 
stances, absorbed by the roots and raised to the leaf, to form proteids and 
other organic substances. In tubers, seeds, parts of stems or leaves where 
starch is stored, it must first be "digested" by the action of some enzyme 
before it can be used as food by the sprouting tubers or germinating seeds. 

For example, starch is converted to a glucose by the action of a diastase. 
Cellulose is converted to a glucose by cytase. Albuminoids are converted 
into available food by a tryptic ferment. Fatty oils are converted into 
glucose and other products by lipase. 

Inulin, a carbohydrate closely related to starch, is stored up for food in 
solution in many composite plants, as in the artichoke, the root tuber of 
dahlia, etc. When used for food by the growing plant it is converted into 
glucose by an enzyme, inulase. Make a section of a portion of a dahlia 
tuber or artichoke and treat with alcohol. The inulin is precipitated intq 
spheero crystals. (See also paragraphs 156-161 and 216&.) 



now plants obtain their food. 109 

218. Then there ara certain fungi which feed on starch or other organic 
substances whether in the host or not, which excrete certain enzymes to 
dissolve the -starch, etc., to bring it into a soluble form before they can 
absorb it as food. Such a process is a sort of extracellular digestion, i.e., 
the organism excretes the enzyme and digests the solid outside, since it 
cannot take the food within its cells in the solid form. To a certain degree 
the higher plants perform also extracellular digestion in the action of root- 
hair excretion on insoluble substances, and in the case of the humus sapro- 
phytes. But for them soluble food is largely prepared by the action of 
acids, etc., in the soil or water, or by the work of fungi and bacteria as 
described in Chapter 9. 

219. Assimilation. — In plant physiology the term assimilation has been 
chiefly used for the process of carbon-dioxide assimilation (= photosyn- 
thesis). Some objections have been raised against the use of assimilation 
here as one of the life processes of the plant, since its inception stages are 
due to the combined action of light, an external factor, and chlorophyll in 
the plant along with the living chloroplastid. So long, however, as it is 
not known that this process can take place without the aid of the living 
plant, it does not seem proper to deny that it is altogether not a process of 
assimilation. It is not necessary to restrict the term assimilation to the 
formation of new living matter in the plant cell; it can be applied also to 
the synthetic processes in the formation of carbohydrates, proteids, etc., 
and called synthetic assimilation. The sun supplies the energy, which is 
absorbed by the chlorophyll, for splitting up the carbonic acid, and the 
living chloroplast then assimilates by a synthetic process the carbon, hydro- 
gen, and oxygen. This process then can be called photo synthetic assimi- 
lation. The nitrite and nitrate bacteria derive energy in the process of 
nitrification, which enables them to assimilate C0 2 from the air, and this is 
called chemo synthetic assimilation. The inorganic material in the form 
of mineral salts, nitrates, etc., absorbed by the root, and carried up to the 
leaves, here meets with the carbohydrates manufactured in the leaf. Under 
the influence of the protoplasm synthesis takes place, and proteids and 
other organic compounds are built up by the union of the salts, nitrates, 
etc., with the carbohydrates. This is also a process of synthetic assimila- 
tion. These are afterward stored as food, or assimilated by the proto- 
plasm in the making of new living matter, or perhaps without the first 
process of synthetic assimilation some of the inorganic salts, nitrates, and 
carbohydrates meeting in the protoplasm are assimilated into new living 
matter directly. 



CHAPTER XI. 



RESPIRATION 



220. One of the life processes in plants which is extremely 
interesting, and which is exactly the same as one of the life proc- 
esses of animals, is easily demonstrated in several ways. 

221. Simple experiment to demonstrate the evolntion of 
C0 2 during germination. — Where there are a number of stu- 
dents and a number of large cylinders are not 
at hand, take bottles of a pint capacity and 
place in the bottom some peas soaked for 12 to 
24 hours. Cover with a glass plate which has 
been smeared with vaseline to make a tight 
joint with the mouth of the bottle. Set aside 
in a warm place for 24 hours. Then slide 
the glass plate a little to one side and quickly 
pour in a little baryta water so that it will run 
down on the inside of the bottle. Cover the 
bottle again. Note the precipitate of barium 
carbonate which demonstrates the presence of 

Test for presence of C0 2 in the bottle. Lower a lighted taper. It 

carbon dioxide in ves- . . , , . - ,. 

sei with germinating is extinguished because oi the great quantity 
of C0 2 . If flower buds are accessible, place 
a small handful in each of several jars and treat the same as in 
the case of the peas. Young growing mushrooms are excellent 
also for this experiment, and serve to show that respiration takes 
place in the fungi. 

no 




Fig. ioi. 



RESPIRA TION. 



Ill 



222. If we now take some of the baryta water and blow our 
"breath" upon it the same film will be formed. The carbon 
dioxide which we exhale is absorbed by the baryta water, and 
forms barium carbonate, just as in the case of the peas. In the 
case of animals the process by which oxygen is taken into the 
body and carbon dioxide is given off is respiration. The process 
in plants which we are now studying is the same, and also is res- 
piration. The oxygen in the vessel was partly used up in the 
process, and carbon dioxide was given off. (It will be seen that 
this process is exactly the opposite of that which takes place in 
carbon-dioxide assimilation.) 

223. To show that oxygen from the air is used up while 
plants respire. — Soak some wheat for 24 hours in water. 
Remove it from the water and place 

it in the folds of damp cloth or 
paper in a moist vessel. Let it 
remain until it begins to germinate. 
Fill the bulb of a thistle tube with 
the germinating wheat. By the aid 
of a stand and clamp, support the 
tube upright, as shown in fig. 102. 
Let the small end of the tube rest 
in a strong solution of caustic potash 
(one stick caustic potash in two- 
thirds tumbler of water) to which 
red ink has been added to give a 
deep red color. Place a small glass 
plate over the rim of the bulb and 
seal it air-tight with an abundance 
of vaseline. Two tubes can be set 
up in one vessel, or a second one 
can be set up in strong baryta water 
colored in the same way. 

224. The result. — It will be seen that the solution of caustic 
potash rises slowly in the tube ; the baryta water will also, if 
that is used. The solution is colored so that it can be plainly 




Fig. 102. 

Apparatus to show respiration of 
germinating wheat. 



112 



PHYSIOLOGY. 



seen at some distance from the table as it rises in the tube. In 

the experiment from which the figure was made for the accom. 

panying illustration, the solution had risen 

— -„ m 6 hours to the height shown in fig. 102. 

||1 In 24 hours it had risen to the height shown 

1 in fig. 103. 

225. Why the solution of caustic 
potash rises in the tube. — Since no air can 

r-, get into the thistle tube from above or 

below, it must be that some part of the 
air which is inside of the tube is used up 
while the wheat is germinating. From 
our study of germinating peas, we know 
that a suffocating gas, carbon dioxide, is 
given off while respiration takes place. 
The caustic potash solution, or the baryta 
water, whichever is used, absorbs the car- 
bon dioxide. The carbon dioxide is heavier 
than air, and so it settles down in the tube 
where it can be absorbed. 

226. Where does the carbon dioxide 
come from? — We know it comes from the 

growing seedlings. The symbol for carbon dioxide is C0 2 . The 
carbon comes from the plant, because there is not enough in 
the air. Nitrogen could not join with the carbon to make CO2. 
Some oxygen from the air or from the protoplasm of the grow- 
ing seedlings (more probably the latter) joins with some of the 
carbon of the plant. These break away from their association 
with the living substance and unite, making CO2. The oxygen 
absorbed by the plant from the air unites with the living sub- 
stance, or perhaps first with food substances, and from these the 
plant is replenished with carbon and oxygen. After the demon- 
stration has been made, remove the glass plate which seals the 
thistle tube above, and pour in a small quantity of baryta water. 
The white precipitate formed affords another illustration that 
carbon dioxide is released. 



Fig. 103. 
Apparatus to show 
respiration of germinat- 
ing wheat. 



RESPIRA TIOAT. 



"3 




Fig. 104. 

Pea seedlings ; the one 

at the left had no oxygen 

and little growth took 

place, the one at the right 




227. Respiration is necessary for growth.— After performing experiment in 

paragraph 221, ii the vessel has not been open 

too long so that oxygen has entered, we may use 

the vessel for another experiment, or set up a 

new one to be used in the course of 12 to 24 

hours, after some oxygen has been consumed. 

Place some folded damp filter paper on the 

germinating peas in the jar. Upon this place 

one-half dozen peas which have just been 

germinated, and in which the roots are about 

20-25 mm long. The vessel should be covered 

tightly again and set aside in a warm room. 

A second jar with water in the bottom instead in oxygen and growth 

of the germinating peas should be set up as a 

check. Damp folded filter paper should be supported above the water, 

and on this should be placed one- 
half dozen peas with roots of the 
same length as those in the jar 
containing carbon dioxide. 

228. In 24 hours examine and 
note how much growth has taken 
place. It will be seen that the 
roots have elongated but very little 
or none in the first jar, while in 
the second one we see that the 
roots have elongated consider- 
ably, if the experiment has been 
carried on carefully. Therefore 
in an atmosphere devoid of oxygen 
very little growth will take place, 
which shows that normal respira- 
tion with access of oxygen (aerobic 
respiration) is necessary for growth. 

229. Another way of perform- 
ing the experiment. — If we wish 
we may use the following experi- 
ment instead of the simple one 
indicated above. Soak a handful 
of peas in water for 12-24 hours, 
and germinate so that twelve with 
the radicles 20-25 mm long may 
be selected. Fill a test tube with 

vessel of mercury so that there will 




Fig. 105. 
Experiment to show that growth takes 
place more rapidly in presence of oxygen 
than in absence of oxygen. The two tubes 
in the vessel represent the condition at the 
beginning of the experiment. At the close 
of the experiment the roots in the tube at 
the left were longer than those in the tube 
filled at the start with mercury. The tube 
outside of the vessel represents the condi- 
tion of things where the peas grew in ab- 
sence of oxygen ; the carbon dioxide given 
off has displaced a portion of the mercury. 
This also shows anaerobic respiration. 

mercury and carefully invert it in 



114 PHYSIOLOGY. 

be no air in the upper end. Now nearly fill another tube and invert in the 
same way. In the latter there will be some air. Remove the outer coats 
from the peas so that no air will be introduced in the tube filled with the 
mercury, and insert them one at a time under the edge of the tube beneath 
the mercury, six in each tube, having first measured the length of the radicles . 
Place in a warm room. In 24 hours measure the roots. Those in the air 
will have grown considerably, while those in the other tube will have grown 
but little or none. 

230. Anaerobic respiration. — The last experiment is also an excellent 
one to show anaerobic respiration. In the tube filled with mercury so tha 
when inverted there will be no air, it will be seen after 24 hours that a gas 
has accumulated in the tube which has crowded out some of the mercury. 
With a wash bottle which has an exit tube properly curved, some water 
may be introduced in the tube. Then insert underneath a small stick of 
caustic potash. This will form a solution of potash, and the gas will be 
partly or completely absorbed. This shows that the gas was carbon di- 
oxide. This evolution of carbon dioxide by living plants when there is no 
access of oxygen is anaerobic respiration (sometimes called intramolecular 
respiration). It occurs markedly in oily seeds and especially in the yeast 
plant. 

231. Energy set free during respiration. — From what we have learned of 
the exchange of gases during respiration we infer that the plant loses carbon 
during this process. If the process of respiration is of any benefit to the 
plant, there must be some gain in some direction to compensate the plant 
for the loss of carbon which takes place. 

It can be shown by an experiment that during respiration there is a 
slight elevation of the temperature in the plant tissues. The plant then 
gains some heat during respiration. Energy is also manifested by growth. 

232. Bespiration in a leafy plant. — We may take a potted plant which 
has a well-developed leaf surface and place it under a tightly fitting bell jar. 

Under the bell jar there also should be placed 
a small vessel containing baryta water. A sim- 
ilar apparatus should be set up, but with no 
plant, to serve as a check. The experiment must 
be set up in a room which is not frequented by 
persons, or the carbon dioxide in the room from 
respiration will vitiate the experiment. The bell 
jar containing the plant should be covered with 
a black cloth to prevent carbon assimilation. In 

Test for Hberatfon of car- the COUrSe ° f IO OT I2 h ° UrS ' if everything has 
bon dioxide from leaf y plant worked properly, the baryta water under the jar 
watei? ln Spl sma < ller vesseL with the plant will show the film of barium ca*-- 
(Sachs.) bonate, while the other one will show none. Res- 

piration, therefore, takes place in a leafy plant as well as in germinating see4» 




RESPtRA Tioisr. 



US 



233. Respiration in fungi. — If several large actively growing mushrooms 
are accessible, place them in a tall glass jar as described for determining 
respiration in germinating peas. In the course of 12 hours test with the 
lighted taper and the baryta water. Respiration takes place in fungi as 
well as in green plants. 

234. Respiration in plants in general. — Respiration is general in all 
plants, though not universal. There are some exceptions in the lower 
plants, notably in certain of the bacteria, which can only grow and thrive 
in the absence of oxygen. 

235. Respiration a breaking-down process. — We have seen that in res- 
piration the plant absorbs oxygen and gives off carbon dioxide. We should 
endeavor to note some of the effects of respiration on the plant. Let us 
take, say, two dozen dry peas, weigh them, soak for 12-24 hours in water, 
and, in the folds of a cloth kept moist by covering with wet paper or sphag- 
num, germinate them. When well germinated and before the green color 
appears dry well in the sun, or with artificial heat, being careful not to burn 
or scorch them. The aim should be to get them about as dry as the seed 
were before germination. Now weigh. The 
germinated seeds weigh less than the dry peas. 
There has then been a loss of plant substance 
during respiration. 

236. Fermentation of yeast. — Take two fer- 
mentation tubes. Fill the closed tubular parts 
of each with a weak solution of grape sugar, or 
with potato decoction, leaving the open bulb 
nearly empty. Into the liquid of one of the 
tubes place a piece of compressed yeast as large 
as a pea. If the tubes are kept in a warm place 
for 24 hours bubbles of gas may be noticed 
rising in the one in which the yeast was placed, 
while in the second tube no such bubbles appear, 
especially if the filled tubes are first sterilized. 
The tubes may be kept until the first is entirely 
filled with the gas. Now dissolve in the liquid 
a small piece of caustic potash. Soon the 
gas will begin to be absorbed, and the liquid 
will rise until it again fills the tube. The gas 
was carbon dioxide, which was chiefly pro- 
duced during the anaerobic respiration of the 
rapidly growing yeast cells. In bread making 
this gas is produced in considerable quantities, and rising through the 
dough fills it with numerous cavities containing gas, so that the bread 
"rises." When it is baked the heat causes the gas in the cavities to ex- 




Fig. 107. 
Fermentation tube with 
culture of yeast. 



u6 



PHYSIOLOGY. 



pand greatly. This causes the bread to "rise" more, and baked in 
this condition it is "light." There are two special processes accom- 
panying the fermentation by yeast: ist, the evolution of carbon dioxide 
as shown above; and, 2d, the formation of alcohol. The best illus- 
tration of this second process is the brewing of beer, where a form of 
the same organism which is employed in "bread rising" is used to "brew 
beer." 

237. The yeast plant. — Before the caustic potash is placed in the tube 
some of the fermented liquid should be taken for study of the yeast plant, 

unless separate cultures are made for this pur- 
pose. Place a drop of the fermented liquid 
on a glass slip, place on this a cover-glass, and 
examine with the microscope. Note the min- 
ute oval cells with granular protoplasm. These 
are the yeast plant. Note in some a small 
"bud" at one side of the end. These buds 
increase in size and separate from the parent 
plant. The yeast plant is one celled, and 
multiplies by "budding" 
or "sprouting." It is a 
fungus, and some species 
of yeast like the present 
one do not form any my- 
celium. Under certain 
conditions, which are not 
very favorable for growth 
- haro- (example, when the yeast is 
myces ceriviseae. a, grown in a weak nutrient 
small colony; b, single ,. . 

cell budding; c, single substance on a thin layer 
cell forming an ascus f p l aste r Paris slab), 
with four spores; a, r y > 

spores free from the several spores are formed 
ascus. (After Rees.) . , . .. 

m many of the yeast cells. 

After a period of rest these spores, will sprout and produce the yeast plant 
again. Because of this peculiar spore formation some place the yeast 
among the sac fungi. (See classification of the fungi.) 

238. Organized ferments and unorganized ferments. — An organism 
like the yeast plant which produces a fermentation of a liquid with evo- 
lution of gas and alcohol is sometimes called a ferment, or ferment or- 
ganism, or an organized ferment. On the other hand the diastatic fer- 
ments or enzymes like diastase, taka diastase, animal diastase (ptyalin in 
the saliva), cytase, etc., are unorganized ferments. In the case of these 
it is better to say enzyme and leave the word ferment for the ferment 
organisms. 





Fig. 108. 
Fermentation tube filled 
with CO2 from action of 
yeast in a sugar solution. 



RES P IRA TIO.V. 



117 



239. Importance of green plants in maintaining purity of air. — By respi- 
ration, especially of animals, the air tends to become " foul " by the increase 
ofC0 2 . Green plants, i.e., plants with chlorophyll, purify the air during 
photosynthesis by absorbing CQ 2 and giving off oxygen. Animals absorb 
in respiration large quantities of oxygen and exhale large quantities of C0 2 . 
Plants absorb a comparatively small amount of oxygen in respiration and 
give off a comparatively small amount of C0 2 . But they absorb during 
photosynthesis large quantities of CO, and give off large quantities of oxygen. 
In this way a balance is maintained between the two processes, so that the 
percentage ofC0 2 in the air remains approximately the same, viz., about 
four-tenths of one per cent, while there are approximately 2 1 parts oxygen 
and 79 parts nitrogen 

239a. Comparison of respiration and photosynthesis. 

Carbon dioxide is taken in by the plant and oxygen 
is liberated. 

Starch is formed as a result of the metabolism, or 
chemical change. 

The process takes place only in green plants, and in 
the green parts of plants, that is, in the presence 
of the chlorophyll. (Exception in purple bacte- 
rium. ) 

The process only takes place under the influence oi 
sunlight. 

It is a building-up process, because new plant sub- 
stance is formed. 

Oxygen is taken in by the plant and carbon dioxide 
is liberated. 

Carbon dioxide is formed as a result of the meta- 
bolism, or chemical change. 

The process takes place in all plants whether they 
possess chlorophyll or not (exceptions in anaerobic 
bacteria). 

The process takes place in the dark as well as in 
the sunlight. 

It is a breaking-down process, because disintegra- 
tion of plant substance occurs. 



Starch formation or 
Photosynthesis. 



Respiration. 



CHAPTER XII. 

GROWTH. 

By growth is usually meant an increase in the bulk of the 
plant accompanied generally by an increase in plant sub- 
stance. Among the lower plants growth is easily studied in 
some of the fungi. 

240. Growth in mucor. — Some of the gonidia (often called 
spores) may be sown in nutrient gelatine or agar, or even in 
prune juice. If the culture has been placed in a warm room, in 
the course of 24 hours, or even less, the preparation will be ready 
for study. 

241. Form of the gonidia. — It will be instructive if we first 
examine some of the gonidia which have not been sown in the cul- 
ture medium. We should note their rounded or globose form, as 
well as their markings if they belong to one of the species with 
spiny walls. Particularly should we note the size, and if possible 
measure them with the micrometer, though this would not be 
absolutely necessary for a comparison, if the comparison can be 
made immediately. Now examine some of the gonidia which 
were sown in the nutrient medium. If they have not already 
germinated we note at once that they are much larger than 
those which have not been immersed in a moist medium. 

242. The gonidia absorb water and increase in size before 
germinating. — From our study of the absorption of water or 
watery solutions of nutriment by living cells, we can easily un- 
derstand the cause of this enlargement of the gonidium of the 
mucor when surrounded by the moist nutrient medium. The 
cell-sap in the spore takes up more water than it loses by diffu- 

u8 



GRO WTH. 



II 9 



sion, thus drawing water forcibly through the protoplasmic mem- 
brane. Since it does not filter out readily, the increase in 




Fig. 109. 
Spores of mucor, and different stages of germination. 

quantity of the water in the cell produces a pressure from within 
which stretches the membrane, and the elastic cell wall yields. 
Thus the gonidium becomes larger. 

243. How the gonidia germinate. — We should find at this 
time many of the gonidia extended on one side into a tube-like 
process the length of which varies according to time and tempera- 
ture. The short process thus begun continues to elongate. This 
elongation of the plant is growth, or, more properly speaking, one 
of the phenomena of growth. 

244. The germ tube branches and forms the mycelium. — 
In the course of a day or so branches from the tube will appear. 
This branched form of the threads of the fungus is, as we 
remember, the mycelium. We can still see the point where 
growth started from the gonidium. Perhaps by this time several 
tubes have grown from a single one. The threads of the myce- 
lium near the gonidium, that is, the older portions of them, have 
increased in diameter as they have elongated, though this increase 
in diameter is by no means so great as the increase in length. 
After increasing to a certain extent in diameter, growth in this 
direction ceases, while apical growth is practically unlimited, 
being limited only by the supply of nutriment. 

245. Growth in length takes place only at the end of the 
thread. — If there were any branches on the mycelium when the 



120 PHYSIOLOGY. 

culture was first examined, we can now see that they remain 
practically the same distance from the gonidium as when they 
were first formed. That is, the older portions of the mycelium 
do not elongate. Growth in length of the mycelium is confined 
to the ends of the threads. 

246. Protoplasm increases by assimilation of nutrient 
substances. — As the plant increases in bulk we note that there 
is an increase in the protoplasm, for the protoplasm is very 
easily detected in these cultures of mucor. This increase in the 
quantity of the protoplasm has come about by the assimilation 
of the nutrient substance, which the plant has absorbed. The 
increase in the protoplasm, or the formation of additional plant 
substance, is another phenomenon of growth quite different from 
that of elongation, or increase in bulk. 

247. Growth of roots. — For the study of the growth of roots 
we may take any one of many different plants. The seedlings of 
such plants as peas, beans, corn, squash, pumpkin, etc., serve 
excellently for this purpose. 

248. Roots of the pumpkin. — The seeds, a handful or so, are 
soaked in water for about 1 2 hours, and then placed between 
layers of paper or between the folds of cloth, which must be kept 
quite moist but not very wet, and should be kept in a warm place. 
A shallow crockery plate, with the seeds lying on wet filter paper, 
and covered with additional filter paper, or with a bell jar, an- 
swers the purpose well. 

The primary or first root (radicle) of the embryo pushes its way 
out between the seed coats at the small end. When the seeds are 
well germinated, select several which have the root \-$cm long. 
With a crow-quill pen we may now mark the terminal portion of 
the root off into very short sections as in fig. no. The first mark 
should be not more than imm from the tip, and the others not 
more than imm apart. Now place the seedlings down on damp 
filter paper, and cover with a bell jar so that they will re- 
main moist, and if the season is cold place them in a warm room. 
At intervals of 8 or 10 hours, if convenient, observe them and 
note the farther growth of the root. 



GRO WTH. 



121 



249. The region of elongation. — While the root has elon- 
gated, the region of elongation is not at the tip of the root. It lies 
a little distance back from the tip, beginning at 
about 2 mm from the tip and extending over 
an area represented by from 4-5 of the milli- 
meter marks. The 
root shown in fig. no 
was marked at 10 a.m. 
on July 5. At 6 p.m. 
of the same day, 8 





Fig. no. 

Root of germinating pumpkin, showing region of 

elongation just back of the tip. 



hours later, growth had taken place as shown in the middle 
figure. At 9 a.m. on the following day, 15 hours later, the 
growth is represented in the lower one. Similar experiments 
upon a number of seedlings give the same result : the region of 
elongation in the growth of the root is situated a little distance 
back from the tip. Farther back very little or no elongation 
takes place, but growth in diameter continues for some time, as 
we should discover if we examined the roots of growing pump- 
kins, or other plants, at different periods. 

50. Movement of region of greatest elongation. — In the 
region of elongation the areas marked off do not all elongate 
equally at the same time. The middle spaces elongate most 
rapidly and the spaces marked off by the 6, 7, and 8 mm marks 
elongate slowly, those farthest from the tip more slowly than the 
others, since elongation has nearly ceased here. The spaces 
marked off between the 2-\mm marks also elongate slowly, but 
soon begin to elongate more rapidly, since that region is becom- 
ing the region of greatest elongation. Thus the region of greatest 
elongation moves forward as the root grows, and remains ap- 
proximately at the same distance behind the tip. 



Is* 



251. Formative region. — If we make a longitudinal section of the tip of a 
growing root of the pumpkin or other seedling, and examine it with the mi- 



122 PH YSIOL OGY. 

croscope, we see that there is a great difference in the character of the 
cells of the tip and those in the region of elongation of the root. First there 
is in the section a V-shaped cap of loose cells which are constantly being 
sloughed off. Just back of this tip the cells are quite regularly isodiametric, 
that is, of equal diameter in all directions. They are also very rich in pro- 
toplasm, and have thin walls. This is the region of the root where new cells 
are formed by division. It is the formative region. The cells on the outside 
of this area are the older, and pass over into the older parts of the root and root 
cap. If we examine successively the cells back from this formative region 
we find that they become more and more elongated in the direction of the 
-axis of the root. The elongation of the cells in this older portion of the root 
explains then why it is that this region of the root elongates more rapidly 
than the tip. 

252. Growth of the stem. — We may use a bean seedling 
growing in the soil. At the junction of the leaves with the stem 
there are enlargements. These are the nodes, and the spaces on 
the stem between successive nodes are the internodes. We should 
mark off several of these internodes, especially the younger ones, 
into sections about $mm long. Now observe these at several 
times for two or three days, or more. The. region of elongation 
is greater than in the case of the roots, and extends back farther 
from the end of the stem. In some young garden bean plants 
the region of elongation extended over an area of 40mm in one 
internode. See also Chapters 38, 39. 

253. Force exerted by growth. — One of the marvelous things connected 
with the growth of plants is the force which is exerted by various members of 
the plant under certain conditions. Observations on seedlings as they are 
pushing their way through the soil to the air often show us that considerable 
force is required to lift the hard soil and turn it to one side. A very striking 
illustration may be had in the case of mushrooms which sometimes make 
their way through the hard and packed soil of walks or roads. That succu- 
lent and tender plants should be capable of lifting such comparatively heavy 
weights seems incredible until we have witnessed it. Very striking illustra- 
tions of the force of roots are seen in the case of trees which grow in rocky 
situations, where rocks of considerable weight are lifted, or small rifts in 
large rocks are widened by the lateral pressure exerted by the growth of a 
root, which entered when it was small and wedged its way in. 

254. Zone of maximum growth. — Great variation exists in the rapidity of 
growth even when not influenced by outside conditions. In our study of the 
elongation of the root we found that the cells just back of the formative region 



GROWTH. 



23 



elongated slowly at first. The rapidity of the elongation of these cells in- 
creases until it reaches the maximum. Then the rapidity of elongation les- 
sens as the cells come to lie farther from the tip. The period of maximum 
elongation here is the zone of maximum growth of these cells. 

255. Just as the cells exhibit a zone of maximum growth, so the members of 
the plant exhiDit a similar zone of maximum growth. In the case of leaves, 
when they are young the rapidity of growth is comparatively slow, then it 
increases, and finally diminishes in rapidity again. So it is with the stem. 
When the plant is young the growth is not so rapid; as it approaches middle 
age the rapidity of growth increases; then it declines in rapidity at the close 
of the season. 

256. Energy of growth. — Closely related to the zone of maximum growth is 
what is termed the energy of growth. This is manifested in the compara- 
tive size of the members of a given plant. 
To take the sunflower for example, the 
lower and first leaves are comparatively 
small. As the plant grows larger the 
leaves are larger, and this increase in 
size of the leaves increases up to a maxi- 
mum period, when the size decreases 
until we reach the small leaves at the top 
of the stem. The zone of maximum growth 
of the leaves corresponds with the maxi- 
mum size of the leaves on the stem. The 
rapidity and energy of growth of the stem 
is also correlated with that of the leaves, 

and the zone of maximum 
growth is coincident with 
that of the leaves. It would 
be instructive to note it 
in the case of other plants 
and also in the case of 
fruits. 

257. Nutation. — During the growth of the stem all of the cells of a given 
section of the stem do not elongate simultaneously. For example the cells 
at a given moment on the south side are elongating more rapidly than the 
cells on the other side. This will cause the stem to bend slightly to the 
north. In a few moments later the cells on the west side are elongating more 
rapidly, and the stem is turned to the east ; and so on, groups of cells in suc- 
cession around the stem elongate more rapidly than the others. This causes 
the stem to describe a circle or ellipse about a central point. Since the re- 
gion of greatest elongation of the cells of the stem is gradually moving toward 
the apex of the growing stem, this line of elongation of the cells which is 




Lex- 



Fig, in. 
uix.ino meter Oels) for measuring elongation of 
the stem during growth. 



124 ^PHYSIOLOGY. 

traveling around the stem does so in a spiral manner. In the same way, 
while the end of the stem is moving upward by the elongation of the cells, 
and at the same time is slowly moved around, the line which the end of the 
stem describes must be a spiral one. This movement of the stem, which is 
common to all stems, leaves, and roots, is nutation. 

258. The importance of nutation to twining stems in their search for a 
place of support, as well as for the tendrils on leaves or stems, will be seen. 
In the case of the root it is of the utmost importance, as the root makes its 
way through the soil, since the particles of soil are more easily thrust aside. 
The same is also true in the case of many stems before they emerge from the 
soil. 



CHAPTER XIII. 

IRRITABILITY. 

259. We should now examine the movements of plant parts 
in response to the influence of certain stimuli. By this 
time we have probably observed that the direction which the 
root and stem take upon germination of the seed is not due to 
the position in which the seed happens to lie. Under normal 
conditions we have seen that the root grows downward and the 
stem upward. 

260. Influence of the earth on the direction of growth. — 
When the stem and root have been growing in these directions 
for a short time let us place the seedling in a horizontal position, 
so that the end of the root extends over an object of support in 
such a way that it will be free to go in any direction. It should 
be pinned to a cork and placed in a moist chamber. In the 
course of twelve to twenty-four hours the root which was formerly 
horizontal has turned the tip downward again. If we should 
mark off millimeter spaces beginning at the tip of the root, we 
should find that the motor zone, or region of curvature, lies in 
the same region as that of the elongation of the root. 

Knight found that the stimulus which influences the root to 
turn downward is the force of gravity. The reaction of the root 
in response to this stimulus is geotropism, a turning influenced 
by the earth. This term is applied to the growth movements of 
plants influenced by the earth with regard to direction. While 
the motor zone lies back of the root tip, the latter receives the 
stimulus and is the perceptive zone. If the root tip is cut off, 
the root is no longer geotropic, and will not turn downward 
when placed in a horizontal position. Growth toward the earth 

"5 



126 



PHYSIOLOGY. 
The lateral growth of secondary roots is dia- 



ls progeotropism. 
geotropism. 

The stem, on the other hand, which was placed in a horizontal 
position has become again erect. This turning of the stem in 





Fig. 112. Fig. 113. 

Germinating pea placed in a hori- In 24 hours gravity has caused the root to 

zontal position. turn downward. 

Figs. 112, 113. — Progeotropism of the pea root. 

the upward direction takes place in the dark as well as in the 
light, as we can see if we start the experiment at nightfall, or 
place the plant in the dark. This up- 
ward growth of the stem is also influ- 
enced by the earth, and therefore is a 
case of geotropism. The special desig- 
nation in the case of upright stems is 
negative geotropism, or apo geotropism, or 
the stems are said 
to be apogeotropic. 




Fig. 114. 
Pumpkin seedling showing apogeotropism. Seedling at the left placed hori- 
zontally, in 24 hours the stem has become erect. 

If we place a rapidly growing potted plant in a horizontal 

position by laying the pot on its side, the ends of the shoots 

will soon turn upward again when placed in a horizontal 

position. Young bean plants growing in a pot began within 
two hours to turn the ends of the shoots upward. 



IRRITABILITY. 



11*] 



Horizontal leaves and shoots can be shown to be subject to 
the same influence, and are therefore diageotropic. 

261. Influence of light. — Not only is light a very important 
factor for plants during photosynthesis, it exerts great influ- 
ence on plant growth and movement. 

262. Growth in the absence of light. — Plants grown in the dark 
are subject to a number of changes. The stems are often longer, 
more slender and 
weaker since they 
contain a larger 
amount of water 
in proportion to 
building material 
which the plant 
obtains from car- 
bohydrates manu- 
factured in the 
light. On many 
plants the leaves 
are very small 
when grown in the 
dark. 

263. Influence of light on direction of 
growth. — While we are growing seedlings, 
the pots or boxes of some of them should be 

placed SO that the plants will have a One- Radish seedlings grown in 

. . „, . , , . the light, shorter, stouter, 

Sided illumination. IhlS Can be done by and green in col or. Growth 

. ... retarded by light. 

placing them near an open window, in a 

room with a one-sided illumination, or they may be placed in a 
box closed on all sides but one which is facing the window or 
light. In 12-24 hours, or even in a much' shorter time in some 
cases, the stems of the seedlings will be directed toward the 
source of light. This influence exerted by the rays of ■ light is 
heliotropism, a turning influenced by the sun or sunlight. 

264. Diaheliotropism. — Horizontal leaves and shoots are 
diaheliotropic as well as diageotropic. The general direction 




Fig. 115. 
Radish seedlings grown in the 
dark, long, slender, not green. 



128 



PHYSIOLOGY, 



which leaves assume under this influence is that of placing them 
with the upper surface perpendicular to the rays of light which 
fall upon them. Leaves, then, exposed to 
the brightly lighted sky are, in general, 
horizontal. This position is taken in direct 
response to the 
stimulus of light. 
The leaves of plants 
with a one-sided illu- 
mination, 
as can be 
seen by 
trial, are 
turned with 

Q A" f F fu II7 'w A ft thdr U PP er 

Seedling of castor-oil bean, before and after £ A 

surfaces to- 
ward the 
source of light, or perpendicular to the in- 
cidence of the light rays. In this way 
light overcomes for the time being the 
direction which growth gives to the leaves. 
The so-called ''sleep" of plants is of 
course not sleep, though the leaves " nod," 
or hang downward, in many cases. There 
are many plants in which we can note 
this drooping of the leaves at nightfall, and in order to prove 
that it is not determined by the time of day we can resort to 
a well-known ex- ===== —————— — — — -—=1 

periment to induce W&MMBRff&&$w^^^^S^R\\ 

this condition dur- 
ing the day. The 
plant which has 
been used to illus- 
trate this is the sun- 
flower. Some of 
these plants, which 





Fig. ii 8. 

Dark chamber with opening at one side to show heliotropism, 
(After Schleichert.) 



IRRITABILIT Y. 



I29 



were grown in a box, when they were about $$ cm m gh were 
.covered for nearly two days, so that the light was excluded. 
At midday on the second day the box was removed, and the 
leaves on the covered plants are well represented by fig. ng, which 
was made from one of them. The leaves of the other plants 
in the box which were not covered were horizontal, as shown 
bv fig. 120. Now on leaving these plants, which had exhibited 




Fig. 120. 
Sunflower plant removed from 
darkness, leaves extending under 
influence of light (diaheliotro- 
pism.) 

induced "sleep" move- 
ments, exposed to the light 
they gradually assumed 
the horizontal position again. 

265. Epinasty and hyponasty. — During 
the early stages of growth of many leaves, 
as in the sunflower plant, the direction of 
growth is different from what it is at a later 
period. The under surface of the young 
leaves grows more rapidly in a longitudinal 
direction than the upper side, so that the 
leaves are held upward close against the 
bud at the end of the stem. This is termed 
hyponasty, or the leaves are said to be 
hyponastic. Later the growth is more rapid 
on the upper side and the leaves turn downward or away from the bud. 
This is termed epinasty, or the leaves are said to be cpinastic. This is shown 
by the night position of the leaves, or in the induced "sleep " of the sun- 



Fig, no. 
Sunflower plant. Epinastic con- 
dition of leaves induced during the 
day in darkness. 



130 



PHYSIOLOG Y. 



flower plant in the experiment detailed above. The day position of the 
leaves on the other hand, which is more or less horizontal, is induced because 
of their irritability under the influence of light, the inherent downward or 
epinastic growth is overcome for the time. Then at nightfall or in darkness, 
the stimulus of light being removed, the leaves assume the position induced 
by the direction of growth. 

266. In the case of the cotyledons of some plants it would seem that the 
growth was hyponastic even after they have opened. The day position of 




Fig. 121. Fig. 122. 

Squash seedling. Position of cotyledons in Squash seedling. Position of cotyledons in 
light. the dark. 

the cotyledons of the pumpkin is more or less horizontal, as shown in fig. 
121. At night, or if we darken the plant by covering with a tight box, the 
leaves assume the position shown in fig. 122. 

While the horizontal position is the general one which is assumed by 
plants under the influence of light, their position is dependent to a certain 
extent on the intensity of the light as well as on the incidence of the light 
rays. Some plants are so strongly heliotropic that they change their posi- 
tions all during the day. 

267. Leaves with a fixed diurnal position. — Leaves of some plants when 
they are developed have a fixed diurnal position and are not subject to 



IRRITABILITY. 



131 



variation. Such leaves tend to arrange themselves in a vertical or para- 
heliotropic position, in which the surfaces are not exposed to the incidence 
of light of the greatest intensity, but to the incidence of the rays of diffused 
light. Interesting cases of the fixed position of leaves are found in the so- 
called compass plants (like Silphium laciniatum, Lactuca scariola, etc.). In 
these the horizontal leaves arrange themselves with the surfaces vertical, and 
also pointing north and south, so that the surfaces face east and west. 

268. Importance of these movements. — Not only are the leaves placed in 
a position favorable for the absorption of the rays of light which are con- 
cerned in making carbon available for food, but they derive other forms of 
energy from the light, as heat, which is absorbed during the day. Then 
with the nocturnal position, the leaves being drooped down toward the stem, 
or with the margin toward the sky, or with the cotyledons as in the pump- 
kin, castor-oil bean, etc., clasped upward together, the loss of heat by 
radiation is less than it would be if the upper surfaces of the leaves were 
exposed to the sky. 

269. Influence of light on the structure of the leaf. — In our study of the 
structure of a leaf we found that in the ivy leaf the palisade cells were on 

the upper surface. This is the case with a 
great many leaves, and is the normal arrange- 
ment of " dorsiventral " leaves which are dia- 
heliotropic. Leaves which are paraheliotropic 
tend to have palisade cells on both surfaces. 
The palisade layer of cells as we have seen is 
made up of cells lying very close together, and 
they thus prevent rapid evaporation. They 
also check to some extent the entrance of the 
rays of light, at least more so than the loose 
spongy parenchyma cells do. Leaves developed 
in the shade have looser palisade and paren- 
chyma cells. In the case of some plants, if 
we turn over a very young leaf, so that the 
under side will be uppermost, this side will 
develop the palisade layer. This shows that 
light has a great influence on the structure of 
the leaf. 

270. Movement influenced by contact. — In 
the case of tendrils, twining leaves, or stems, 
the irritability to contact is shown in a move- 
ment of the tendril, etc., toward the object in 
touch. This causes the tendril or stem to coil 
around the object for support. The stimulus is also extended down the part 
of the tendril below the point of contact (see fig. 123), and that part coils 




Fig. 123. 

Coiling tendril of bryony. 



13^ 



PHYSIOLOGY. 



up like a wire coil spring, thus drawing the leaf or branch from which the 
tendril grows closer to the object of support. This coil between the object 
of support and the plant is also very important in easing up the plant when 
subject to violent gusts of wind which might tear the plant from its support 
were it not for the yielding and springing motion of this coil. 

271. Sensitive plants. — These plants are remarkable for the 
rapid response to stimuli. Mimosa pudica is an excellent plant 
to study for this purpose. 

272. Movement in response to stimuli. — If we pinch with 
the forceps one of the terminal leaflets, or tap it with a pencil, 
the two end leaflets fold above the ' ' vein ' ' of the pinna. This 

is immediately followed 
by the movement of the 
next pair, and so on as 
shown in fig. 125, until all 
the leaflets on this pinna 
are closed, then the stimu- 
lus travels down the 
other pinnae in a simi- 
lar manner, and 

Fig. 124. 
Sensitive-plant leaf 
in normal position. 



Fig. 1 25. 
Pinnas fold- 
ing up after 

stimulus. 





Fig. 126. 



soon the pinnse approximate each other and 
the leaf then drops downward as shown in 
fig. 126. The normal position of the leaf is folded and leaf drooped, 
shown in fig. 124. If we jar the plant by striking it or by jarring 
the pot in which it is grown all the leaves quickly collapse into 
the position shown in fig. 126. If we examine the leaf now we 
see minute cushions at the base of each leaflet, at the junction of 
the pinnae with the petiole, and a larger one at the junction of 
the petiole with the stem. We shall also note that the move- 
ment resides in these cushions. 



IRRITABILITY. 



133 



273. Transmission of the stimulus. — The transmission of 
the stimulus in this mimosa from one part of the plant has been 
found to be along the cells of the bast. 

274, Cause of the movement. — The movement is caused by 
a sudden loss of turgidity on the part of the cells in one portion 
of the pulvinus, as the cushion is called. In the case of the 
large pulvinus at the base of the petiole this loss of turgidity is 
in the cells of the lower surface. There is a sudden change in 
the condition of the protoplasm of the cells here so that they 
lose a large part of their water. This can be seen if with a sharp 
knife we cut off the petiole just above the pulvinus before move- 
ment takes place. A drop of liquid exudes from the cells of the 
lower side. 



275. Paraheliotropism of the leaves of the sensitive plant. — If the mimosa 
plant is placed in very intense light the leaflets will turn their edges toward 
the incidence of the rays of light. This is also true of other plants in 
intense light, and is paraheliotropism. Transpiration is thus lessened, and 
chlorophyll is protected from too intense light. 

We thus see that variations in the intensity of light have an important 
influence in modifying movements. Variations in temperature also exert 

a considerable influence, rapid 
elevation of temperature causing 
certain flowers to open, and 
falling temperature causing 
them to close. 

276. Sensitiveness of insec- 
tivorous plants. — The Venus 
fly-trap (Dionaea muscipula)and 
the sundew (drosera) are in- 
teresting examples of sensitive 
plants, since the leaves close in 
response to the stimulus from 
insects. 




Fig. 126. 
Leaf of Venus fly- 
trap (Dionaea musci- 
pula), showing winged 
petiole and toothed 
lobes. 



Fig. 127. 
Leaf of Drosera ro- 
tundifolia, some of the 
glandular hairs folding 
inward as a result of a 
stimulus. 



277. Hydrotropism. — 

Roots are sensitive to mois- 
ture. They will turn toward moisture. This is of the greatest 
importance for the well-being of the plant, since the roots will seek 
those places in the soil where suitable moisture is present. On 



134 PHYSIOLOGY. 

the other hand, if the soil is too wet there is a tendency for the 
roots to grow away from the soil which is saturated with water. 
In such cases roots are often seen growing upon the surface of 
the soil so that they may obtain oxygen, which is important for 
the root in the processes of absorption and growth. Plants then 
may be injured by an excess of water as well as by a lack of 
water in the soil. 

278 Temperature. — In the experiments on germination thus far made 
it has probably been noted that the temperature has much to do with the 
length of time taken for seeds to germinate. It also influences the 
rate of growth. The effect of different temperatures on the germination of 
seed can be very well noted by attempting to germinate some in rooms at 
various temperatures. It will be found, other conditions being equal, that 
in a moderately warm room, or even in one quite warm, 25-30 degrees cen- 
tigrade, germination and growth goes on more rapidly than in a cool room, 
and here more rapidly than in one which is decidedly cold. In the case of 
most plants in temperate climates, growth may go on at a temperature but 
little above freezing, but few will thrive at this temperature. 

279. If we place dry peas or beans in a temperature of about 70° C. for 15 
minutes they will not be killed, but if they have been thoroughly soaked in 
water and then placed at this temperature they will be killed, or even at a 
somewhat lower temperature. The same seeds in the dry condition will 
withstand a temperature of io° C. below, but if they are first soaked in water 
this low temperature will kill them. 

280. In order to see the effect of freezing we may thoroughly freeze a sec- 
tion of a beet root, and after thawing it out place it in water. The water is 
colored by the cell-sap which escapes from the cells, just as we have seen it 
does as a result of a high temperature, while a section of an unfrozen beet 
placed in water will not color it if it was previously washed. 

If the slice of the beet is placed at about — 6° C. in a shallow glass vessel, 
and covered, ice will be formed over the surface. If we examine it with the 
microscope ice crystals will be seen formed on the outside, and these wLl 
not be colored. The water for the formation of the crystals came from the 
cell-sap, but the concentrated solutions in the sap were not withdrawn by 
the freezing over the surface. 

281. If too much water is not withdrawn from the cells of many plants in 
freezing, and they are thawed out slowly, the water which was withdrawn 
from the cells will be absorbed again and the plant will not be killed. But 
if the plant is thawed out quickly the water will not be absorbed, but will 
remain on the surface and evaporate. Some will also remain in the inter- 
Cellular spaces, and the plant will die, Some plants, howeyer ? no matter how 



IRRITA BILIT Y. 135 

slowly they are thawed out, are killed after freezing, as the leaves of the 
pumpkin, dahlia, or the tubers of the potato. 

282. It has been found that as a general rule when plants, or plant parts, 
contain little moisture they will withstand quite high degrees of tempera- 
ture, as well as quite low degrees, but when the parts are filled with sap or 
water they are much more easily killed. For this reason dry seeds and the 
winter buds of trees, and other plants, because they contain but little water, 
are better able to resist the cold of winters. But when growth begins in the 
spring, and the tissues of these same parts become turgid and filled with 
water, they are quite easily killed by frosts. It should be borne in mind, 
however, that there is great individual variation in plants in this respect, 
some being more susceptible to cold than others. There is also great varia- 
tion in plants as to their resistance to the cold of winters, and of arctic 
climates, the plants of the latter regions being able to resist very low tem- 
peratures. We have examples also in the arctic plants, and those which 
grow in arctic climates on high mountains, of plants which are able to carry 
on all the life functions at temperatures but little above freezing. 

For further discussion as to relation of plants to temperature, see Chap 
ters 46, 48, 49, and 53, 



PART II. 

MORPHOLOGY AND LIFE HISTORY OF REPRE- 
SENTATIVE PLANTS. 

CHAPTER XIV. 

SPIROGYRA. 

283. In our study of protoplasm and some of the processes of 
plant life we became acquainted with the general appearance of 
the plant spirogyra. It is now a familiar object to us. And in 
taking up the study of representative plants of the different 
groups, we shall find that in knowing some of these lower plants 
the difficulties of understanding methods of reproduction and 
relationship are not so great as they would be if we were entire- 
ly ignorant of any members of the lower groups. 

284. Form of spirogyra. — We have found that the plant 
spirogyra consists of simple threads, with cylindrical cells 
attached end to end. We have also noted that each cell of the 
thread is exactly alike, with the exception of certain ' ' hold- 
fasts ' ' on some of the species. If we should examine threads in 
different stages of growth we should find that each cell is capable 
of growth and division, just as it is capable of performing all the 
functions of nutrition and assimilation. The cells of spirogyra 
then multiply by division. Not simply the cells at the ends of 
the threads but any and all of the cells divide as they grow, and 
in this way the threads increase in length. 

285. Multiplication of the threads. — In studying living material of this 
plant we have probably noted that the threads often become broken by two of 
the adjacent cells of a thread becoming separated. This may be and is accom- 

136 



SPIROGYRA. 



137 



plished in many cases without any injury to the cells. In this manner the 
threads or plants of spirogyra, if we choose to call a thread a 
plant, multiply, or increase. In this breaking of a thread the 
cell wall which separates any two cells splits. If we should 
examine several species of spirogyra we would probably find 
threads which present two types as regards the character of 
the walls at the ends of the cells. In fig. 128 we see that the 
ends are plain, that is, the cross walls are all straight. But 
in some other species the inner wall of the cells presents a 
peculiar appearance. This inner wall at the end of the 
cell is at first straight across. But it soon becomes folded 
back into the interior of its cell, just as the end of an 
empty glow finger may be pushed in. Then the infolded 
end is pushed partly out again, so that a peculiar figure is 
the result. 

286. How some of the threads break. — In the separation 
of the cells of a thread this peculiarity is often of advan- 
tage to the plant. The cell-sap within the protoplasmic 
membrane absorbs water and the pressure pushes on the 
ends of the infolded cell walls. The inner wall being so 
much longer than the outer wall, a pull is exerted on the 
latter at the junction of the cells. Being weaker at this 
point the outer wall is ruptured. The turgidity of the two 
cells causes these infolded inner walls to push out suddenly 
as the outer wall is ruptured, and the thread is snapped 
apart as quickly as a pipe-stem may be broken. 

287. Conjugation of spirogyra. — Under cer- 
tain conditions, when vegetative growth and 
multiplication cease, a process of reproduction 
takes place which is of a kind termed sexual repro- 
duction. If we select mats of spirogyra which 
have lost their deep green color, we are likely to 
find different stages of this sexual process, which 
in the case of spirogyra and related plants is called 
conjugation. A few threads of such a mat we 
should examine with the microscope. If the 
material is in the right condition we see in certain 
of the cells an oval or elliptical body. If we 
note carefully the cells in which these oval bodies 
are situated, there will be seen a tube at one side which con- 



gyra, showing long 
cells, chlorophyll 
band, nucleus, 
strands of proto- 
plasm, and the 
granular wall layer 
of protoplasm. 



138 



MORPHOLOGY. 



nects with an empty cell of a thread which lies near as shown in 

fig. 129. If we search through the material we may see other threads 

connected in this ladder fashion, in which 

the contents of the cells are in various stages 

of collapse from what we have seen in the 

growing cell. In some the protoplasm and 

chlorophyll band have moved but little from 

the wall ; in others it forms a mass near the 

center of the cell, and again in others we 

will see that the contents of the cell of one 

of the threads has moved partly through the 

tube into the cell of the thread with which it 

is connected. 

289. This suggests to us that the 
oval bodies found in the cells of one 
thread of the ladder, while the cells 
of the other thread were empty, are 
formed by the union of the contents 
of the two cells. In fact that is what 
does take place. This kind of union 
of the contents of two similar or nearly 
similar cells is conjugation. The oval 
bodies which are the result of this 
conjugation are zygotes, or zygospores. 
When we are examining living ma-. 
terial of spirogyra in this stage it is J) 
possible to watch this process of con- 
jugation. Fig. 130 represents the differ- 
ent stages of conjugation of spirogyra. 

290. How the threads conjugate, or join. — The cells of two 
threads lying parallel put out short processes. The tubes from 
two opposite cells meet and join. The walls separating the con- 
tents of the two tubes dissolve so that there is an open communi- 
cation between the two cells. The content of each one of these 
cells which take part in the conjugation is a gamete. The one 
which passes through the tube to the receiving cell is the supply- 




Fig. I2y. 
Zygospores of spirogyra. 



SPIROGYRA, 



1 39 



ing gamete, while that of the receiving cell is the receiving 

gamete. 

291. How the protoplasm moves from one cell to another. — Before any 
movement of the protoplasm of the supplying cell takes place we can see 




Fig. 130. 
Conjugation in spirogyra ; from left to right beginning in the upper row is shown the 
gradual passage of the protoplasm from the supplying gamete to the receiving gamete. 

that there is great activity in its protoplasm. Rounded vacuoles appear 
which increase in size, are filled with a watery fluid, and swell up like a 
vesicle, and then suddenly contract and disappear. As the vacuole disap- 
pears it causes a sudden movement or contraction of the protoplasm around 
it to take its place. Simultaneously with the disappearance of the vacuole 
the membrane of the protoplasm is separated from a part of the wall. This 
is probably brought about by a sudden loss of some of the water in the cell- 
sap. These activities go on, and the protoplasmic membrane continues to 
slip away from the wall. Every now and then there is a movement by 
which the protoplasm is moved a short distance. It is moved toward the 
tube and finally a portion of it with one end of the chlorophyll band begins 
to move into the tube. About this time the vacuoles can be seen in an 
active condition in the receptive cell. At short intervals movement qqix- 



140 



MORPHOLOG Y. 



tinues until the content of the supplying cell has passed over into that of the 
receptive cell. The protoplasm of this one is now slipping away from the 
cell wall, until finally the two masses round up into the one zygospore. 

292. The zygospore. — This zygospore now acquires a thick wall which 
eventually becomes brown in color. The chlorophyll color fades out, and a 
large part of the protoplasm passes into an oily substance which makes it 
more resistant to conditions which would be fatal to the vegetative threads. 
The zygospores are capable therefore of enduring extremes of cold and dry- 
ness which would destroy the threads. They pass through a ''resting" 
period, in which the water in the pond may be frozen, or dried, and with the 
oncoming of favorable conditions for growth in the spring or in the autumn 
they germinate and produce the green thread again. 

293. Life cycle. — The growth of the spirogyra thread, the conjugation of 
the gametes and formation of the zygospore, and the growth of the thread 
from the zygospore again, makes what is called a complete life cycle. 

294. Fertilization. — While conjugation results in the fusion of the two 
masses of protoplasm, fertilization is accomplished when the nuclei of the 
two cells come together in the zygospore and fuse into a single nucleus. The 








Fig. 131. 
Fertilization in spirogyra ; shows different stages of fusion of the two nuclei, with mature 
zygospore at right. (After Overton.) 

different stages in the fusion of the two nuclei of a recently formed zygospore 
are shown in figure 131. 

In the conjugation of the two cells, the chlorophyll band. of the supplying 
cell is said to degenerate, so that in the new plant the number of chlorophyll 
bands in a cell is not increased by the union of the two cells. 

295. Simplicity of the process. — In spirogyra any cell of the thread 
may form a gamete (excepting the holdfasts of some species). Since all of 
the cells of a thread are practically alike, there is no structural difference 
between a vegetative cell and a cell about to conjugate. The difference is a 
physiological one. All the cells are capable of conjugation if the physiolog- 
ical conditions are present. All the cells therefore are potential gametes. 
(Strictly speaking the wall of the cell is the garnet angium, while the content 
forms the gamete.) 

While there is sometimes a slight difference in size between the conjugate 



SPIROGYRA. 



I 4 I 



ing cells, and the supplying cell may be the smaller, this is not general. We 
say, therefore, that there is no differentiation among the gametes, so that 
usually before the protoplasm begins to move one cannot say which is to be 
the supplying and which the receiving gamete. 

296. Position of the plant spirogyra. — From our study then we see that 
there is practically no differentiation among the vegetative cells, except 
where holdfasts grow out from some of the cells for support. They are all 
alike in form, in capacity for growth, division, or multiplication of the 
threads. Each cell is practically an independent plant. There is no differ- 
entiation between vegetative cell and conjugating cell. All the cells are 
potential gametes. Finally there is no structural differentiation between the 
gametes. This indicates then a simple condition of things, a low grade of 
organization. 

297. The alga spirogyra is one of the representatives of the lower algae 
belonging to the group called Conjugate. Zygnema with star-shaped chloro- 
plasts, mougeotia with straight or sometimes twisted chlorophyll bands, be- 
long to the same group. In the latter genus only a portion of the protoplasm 
of each cell unites to form the zygospore, which is located in the tube between 
the cells. 




Fig. 133- 
Micrasterias. 




Fig. 134. 
Xanthidium. 




Fig. 137. 
Cosmarium. 



298. The desmids also belong to the same group. The desmids usually live 
as separate cells. Many of them are beautiful in form. They grow entangled 
among other algae, or on the surface of aquatic plants, or on wet soil. Sev. 
eral genera are illustrated in figures 132-137. 



CHAPTER XV. 

VAUCHERIA. 

299. The plant vaucheria we remember from our study in 
an earlier chapter. It usually occurs in dense mats floating 
on the water or lying on damp soil. The texture and feeling of 
these mats remind one of "felt," 
and the species are sometimes called 
the " green felts." The branched 
threads are continuous, that is there 
are no cross walls in the vegetative 
threads. This plant multiplies it- 
self in several ways which would 
be too tedious to detail here. But 
when fresh bright green mats can be 
obtained they should be placed in 
a large vessel of water and set in 
a cool place. Only a small amount 
of the alga should be placed in a 
vessel, since decay 
will set in more 
rapidly with a large 
quantity. For 

several days one 
should look for 

small green bodies which may be floating at the side of the vessel 
next the lighted window. 

300. Zoogonidia of vaucheria. — If these minute floating green bodies are 
found, a small drop of water containing them should be mounted for exami- 

142 




r ig. 138. 
Portion of branched thread o. 



■auchena 



VAUCHERIA, 



H3 



nation. If they are rounded, with slender hair-like appendages over the 
surface, which vibrate and cause motion, they very likely are one of the 
kinds of reproductive bodies of vaucheria. The hair-like appendages are 
cilia, and they occur in pairs, several of them distributed over the surface. 
These rounded bodies are gonidia, and because they are motile they are 
called zoogonidia. 

By examining some of the threads in the vessel where they occurred we 
may have perhaps an opportunity to see how they are produced. Short 
branches are formed on the threads, and the contents are separated from 
those of the main thread by a septum. The protoplasm and other contents of 
this branch separate from the wall, round up into a mass, and escape through 
an opening which is formed in the end. Here they swim around in the 
water for a time, then come to rest, and germinate by growing out into a 
tube which forms another vaucheria plant. It will be observed that this 
kind of reproduction is not the result of the union of two different parts of 
the plant. It thus differs from that which is termed sexual reproduction. A 
small part of the plant simply becomes separated from it as a special body, 
and then grows into a new plant, a sort of multiplication. This kind of re- 
production has been termed asexual reproduction. 

301. Sexual reproduction in vaucheria. — The organs which are concerned 
in sexual reproduction in vaucheria are very readily obtained for study if 
one collects the material at the right season. They are found quite readily 
during the spring and autumn, and may be preserved in formalin for study 
at any season, if the material cannot be collected fresh at the time it is 
desired for study. Fine material for study often occurs on the soil of pots in 

greenhouses during the winter. 
While the zoogonidia are more 
apt to be found in material 
which is quite green and fresh- 
ly growing, the sexual organs 
are usually more abundant 
when the threads appear some- 
what yellowish, or yellow 
green. 




Fig- 139. 



302. Vaucheria sessi- 
lis; the sessile vauche- 

Young anthcridium and oogonium of Vaucheria ses- . T , . . , 

silis, before separation from contents of thread by a Tia. In TillS plant me 

septum. t -i 

sexual organs are sessile, 
that is they are not borne on a stalk as in some other species. 
The sexual organs usually occur several in a group. Fig. 139 
represents a portion of a fruiting plant. 



H4 



MORPHOLOGY. 



303. Sexual organs of vaucheria. Anther idium. — The 

antheridia are short, slender, curved branches from a main 
thread. A septum is formed which separates an end portion 
from the stalk. This end cell is the antheridium. Frequently it 
is collapsed or empty as shown in fig. 140. The protoplasm in 




Fig. 140. 
Vaucheria sessilis, one antheridium between two oogonia. 

the antheridium forms numerous small oval bodies each with two 
slender lashes, the cilia. When these are formed the antherid- 
ium opens at the end and they escape. It is after the escape 
of these spermatozoids that the antheridium is collapsed. Each 
spermatozoid is a male gamete. 

304. Oogonium. — The oogonia are short branches also, but 
they become large and , % 

somewhat oval. The / * 

septum which separates the 
protoplasm from that of 
the main thread is as we 
see near the junction of 
the branch with the main 
thread. The oogonium, 
as shown in the figure, is 
usually turned somewhat 
to one side. When mature the pointed end opens and a bit of the 
protoplasm escapes. The remaining protoplasm forms the large 
rounded egg cell which fills the wall of the oogonium. In some 
of the oogonia which we examine this egg is surrounded by a 
thick brown wall, with starchy and oily contents. This is the 




Fig. 141. 
Vaucheria sessilis ; oogonium opening and emit- 
ting a bit of protoplasm ; spermatozoids ; sperma- 
tozoids entering oogonium. (After Pringsheim and 
Goebel.) 



VA UCHERIA. 



145 



fertilized egg (sometimes called here the oospore) . It is freed 
from the oogonium by the disintegration of the latter, sinks into 




Fig. 142. 
Fertilization in vaucheria. inn, male nucleus ; fn, female nucleus. Male nucleus entering 
the egg and approaching the female nucleus. (After Oltmans.) 

the mud, and remains here until the following autumn or spring, 
when it grows directly into a new plant. 

305. Fertilization. — Fertilization is accomplished by the 
spermatozoids swimming in at the open end of the oogonium, 



x t£&£&*%k 



,#\. 



Wm 



KHtn 



"*^\ 



*r 






Fig. 143. 
Fertilization of vaucheria. /«, female nucleus; /««, male nucleus. The different figures 
show various stages in the fusion of the nuclei. 

when one of them makes its way down into the egg and fuses 
with the nucleus of the egg. 

306. The twin vaucheria (V. geminata). — Another species of vaucheria 
is the twin vaucheria. This is also a common one, and may be used for 
jtudy instead of the sessile vaucheria if the latter cannot be obtained. The 
sexual organs are borne at the end of a club-shaped branch. There are 
usually two oogonia, and one antheridium between them which terminates 
the branch. In a closely related species, instead of the two oogonia there is 
a whorl of them with the antheridium in the center. 

307. Vaucheria compared with spirogyra. — In vaucheria we have a plant 
'hich is very interesting to compare with spirogyra in several respects. 



t46 



MORPHOLOGY. 



Growth takes place, not in all parts of the thread, but is localized at the ends 
of the thread and its branches. This represents a distinct advance on such 
a plant as spirogyra. Again, only specialized parts of the plant in vaucheria 
form the sexual organs. These are short branches. Farther there is a great 
difference in the size of the two organs, and especially in the size of the 
gametes, the supplying gametes (spermatozoids) being very minute, 
while the receptive gamete is large and contains all the nutriment for the 
fertilized egg. In spirogyra, on the other hand, there is usually no differ- 
ence in size of the gametes, as we have seen, and each contributes equally in 
the matter of nutriment for the fertilized egg. Vaucheria, therefore, rep- 
resents a distinct advance, not only in the vegetative condition of the plant, 
but in the specialization of the sexual organs. Vaucheria, with other related 
algae, belongs to a group known as the Siphonece, so called because the plants 
are tube-like or siphon-like* 

308. Botrydium granulatum. — An example of one of the simpler 

members of the Siphoneas is 
Botrydium granulatum. It is 
found sometimes in abundance 
on wet ground which is colored 
green or red by its presence, 
according to the stage of de- 
velopment. The plant body is 
long pear-shaped, the smaller 
end attached to the ground, by 
slender branched rhizoids (Fig. 
143). The protoplasm contains 
many nuclei and lines the inside 
of the wall. When multiplication 
takes place large numbers of 
small zoospores with one cilium 
each are formed in the proto- 
plasm, and escape at free end. 
Reproduction takes place by 
two-ciliated gametes, which fuse 
in pairs to form zygospores. In 
dry seasons the protoplasm in 
the pear-shaped plant passes 
down into the rhizoids and 
forms small rounded planospores. 
All the stages of development are too complicated to describe here. 




Botrydium granulatum. A, the whole 
plant; B, swarm spore; C, planogametes ; a, 
a single gamete; b-e, two gametes in process 
of fusion; f, zygote. 



CHAPTER XVI. 

CEDOGONIUM. 

309. (Edogonium is also an alga. The plant is sometimes 
associated with spirogyra, and occurs in similar situations. Our 
attention was called to it in the study of chlorophyll bodies. 
These we recollect are, in this plant, small oval disks, and thus 
differ from those in spirogyra. 

310. Form of cedogonium. — Like spirogyra, cedogonium 
forms simple threads which are made up of cylindrical cells 
placed end to end. But the plant is very different from any 
member of the group to which spirogyra belongs. In the first 
place each cell is not the equivalent of an individual plant as in 
spirogyra. Growth is localized or confined to certain cells of 
the thread which divide at one end in such a way as to leave a 
peculiar overlapping of the cell walls in the form of a series of 
shallow caps or vessels (fig. 144), and this is one of the character- 
istics of this genus. Other differences we find in the manner of 
reproduction. 

311. Fruiting stage of cedogonium. — Material in the fruiting 
stage is quite easily obtainable, and may be preserved for study 
in formalin if there is any doubt about obtaining it at the time 
we need it for study. This condition of the plant is easily de- 
tected because of the swollen condition of some of the cells, or 
by the presence of brown bodies with a thick wall in some of the 
cells. 

312. Sexual organs of cedogonium. Oogonium and egg. — 
The enlarged cell is the oogonium, the wall of the cell being the 
wall of the oogonium. (See fig. 145.) The protoplasm inside, before 

147 



148 



MORPHOLOG V. 



fertilization, is the egg cell. In those cases where the brown body 

with a thick wall is present fertilization has taken place, and this 

body is Xhe fertilized egg, or oospore. It contains 

large quantities of an oily substance, and, like 




Fig. 144. 

Portion o f 
thread of cedo- 
gonium, show- 
ing chlorophyll 
grains, and pe- 
culiar cap cell 
walls. 




Fig. 145. 
CEdogonium undulatum, with oogonia and dwarf males; 
the upper oogonium at the right has a mature, oospore. 



the fertilized egg of spirogyra and vaucheria, is able to with- 
stand greater changes in temperature than the vegetative stage, 
and can endure drying and freezing for some time without 
injury. 

In the oogonium wall there can frequently be seen a rift near 
the middle of one side, or near the upper end. This is the 



CEDOGONIUM. 



149 



opening through which the spermatozoid entered to fecundate 
the egg. 

313. Dwarf male plants. — In some species there will also be 
seen peculiar club-shaped dwarf plants attached to the side of the 
oogonium, or near it, and in many cases the end of this dwarf 
plant has an open lid on the end. 

314. Antheridium. — The end cell of the dwarf male in such 
species is the antheridium. In other species the spermatozoids 
are developed in different cells (antheridia) of the same thread 
which bears the oogonium, or on a different thread. 



315. Zoospore stage of oedogonium. — The egg after a period of rest starts 
into active life again. In doing so it does not develop the thread-like plant 
directly as in the case of vaucheria and spirogyra. It first divides into four 
zoospores which are exactly like the zoogonidia in form. (See fig. 152.) 
These germinate and develop the thread form again. This is a quite re- 
markable peculiarity of oedogonium when compared with either vaucheria 
or spirogyra. It is the introduction of an intermediate stage between the 
fertilized egg and that form of the plant which bears the sexual organs, and 
should be kept well in mind. 

316. Asexual reproduction. — Material for the study of this stage of oedo- 
gonium is not readily obtainable just when we wish it for study. But fresh 
plants brought in and placed in a 
quantity of fresh water may yield 
suitable material, and it should be 
examined at intervals for several 
days. This kind of reproduction 
takes place by the formation of 
zoogonidia. The entire contents 
of a cell round off into an oval 
body, the wall of the cell breaks, 
and the zoogonidium escapes. It 
has a clear space at the small 
end, and around this clear space 
is a row or crown of cilia as shown in fig. 146. By the vibration of these cilia 
the zoogonidium swims around for a time, then settles down on some object of 
support, and several slender holdfasts grow out in the form of short rhizoids 
which attach the young plant. 

317. Sexual reproduction. Antheridia. — The antheridia are short cells 
which are formed by one of the ordinary cells dividing into a number of 
disk-shaped ones as shown in fig. 147. The protoplasm in each antheridium 





Fig. 146. 
Zoogonidia of oedogonium escaping. 
At the right one is germinating and 
forming the holdfasts, by means of which 
these algae attach themselves to objects 
for support. (After Pringsheim.) 



i5o 



MORPHOLOG Y. 



forms two spermatozoids (sometimes only one) which are of the same form as 
the zoogonidia but smaller, and yellowish instead of green. In some species 

a motile body intermedi- 
ate in size and color be- 
tween the spermatozoids 
and zoogonidia is first 
formed, which after 
swimming around comes 
to rest on the oogonium, 
or near it, and develops 
what is called a " dwarf 
male plant " from which 
the real spermatozoid is 
produced. 

PortJonhfdof cede- 318 : 00 S° ni »- - The 

go nium showing upper half oogonia are formed di- 
of egg open, and a sperma- ,, j. r ,, 

tozoid ready to enter. (After rectl 7 from One of the 
Klebahn). vegetative cells. Inmost 

species this cell first enlarges in diameter, so that it is easily detected. The 
protoplasm inside is the egg cell. The oogonium wall opens, a bit of the 
protoplasm is emitted, and the spermatozoid then enters and fertilizes it 
(fig. 148). Now a hard brown wall is formed around it, and, just as in spirogyra 




Fig. 147. 
Portion of thread 
o f oedogonium 
showing antheridia 





Fig. 140. 
Male nucleus just entering 
egg at left side. 




Fig. 1 si- 
Male nucleus fusing with The two nuclei fused, and 
female nucleus. fertilization complete. 



Figs. 149-151. — Fertilization in cedogonium. (After Klebahn). 



and vaucheria, it passes through a resting period. At the time of germination 
it does not produce the thread-like plant again directly, but first forms four 
zoospores exactly like the zoogonidia (fig. 152). These zoospores then 
germinate and form the plant. 

319. (Edogonium compared with spirogyra. — Now if we compare cedo- 
gonium with spirogyra, as we did in the case of vaucheria, we find here also 
that there is an advance upon the simple condition which exists in spiro- 
gyra. Growth and division of the thread is limited to certain portions. The 
sexual organs are differentiated. They usually differ in form and size from 
the vegetative cells, though the oogonium is simply a changed vegetative 



CEDOGONIUM. 



151 



cell. The sexual organs are differentiated among themselves, the antheridium 
is small, and the oogonium large. The gametes are also differentiated in 
size, and the male gamete is motile, and carries in its body the nucleus 
which fuses with the nucleus of the egg cell. 

But a more striking advance is the fact that the fertilized egg does not 




Fig. J52. 




Fertilized egg of oedogonium after a period of rest escaping from the wall of the oogonium, 
and dividing into the four zoospores. (After Juranyi.) 




produce the vegetative thread of oedogonium directly, but first forms four 
zoospores, each of which is then capable of developing into the thread. On 
the other hand we found 
that in spirogyra the zygo- 
spore develops directly 
into the thread form of the 
plant. 

320. Position of oedo- 
gonium. — CEdogonium is 
one of the true thread-like 
algae, green in color, and 
the threads are divided 
into distinct cells. It, 
along with many relatives, 
was once placed in the old 

genus conferva. These are all now placed in the group 
Confcrvoidc'ce, that is, the conferva -like alg<r. p- 

321. Relatives of oedogonium. — Many other genera Portion of chaetophora 
are related to oedogonium. Some consist of simple showing branching, 
threads, and others of branched threads. An example of the branched 
forms is found in chaetophora, represented in figures 153, 154. This plant 
grows in quiet pools or in slow-running water. It is attached to sticks, rocks, 
or to larger aquatic plants. Many threads spring from the same point of 
attachment and radiate in all directions. This, together with the branching 
of the threads, makes a small, compact, greenish, rounded mass, which is 



Fig. 153. 

Tuft of chaeto- 
phora, natural 




1 5 2 MORPHOL OGY. 

held firmly together by a gelatinous substance. The masses in this species 
are about the size of a small pea, or smaller. Growth takes place in chae- 
tophora at the ends of the threads and branches. That is, growth is api- 
cal. This, together with the branched threads and the tendency to form 
cell masses, is a great advance of the vegetative condition of the plant upon 
that which we find in the simple threads of cedogonium. 



CHAPTER XVII. 

COLEOCHyETE. 



322. Among the green algae coleochsete is one of the most 
interesting. Several species are known in this country. One 
of these at least should be examined if it is possible to obtain it. 
It occurs in the water of fresh lakes and ponds, attached to 
aquatic plants. 

323. The shield-shaped coleochsete. — This plant (C. scutata) 






Fig- 155. 

Stem o f 
aquatic plant 
showing co- 
leo chae t e, 
natural size. 




Fig. 156. 
Thallus of Coleochaste scutata. 



is in the form of a flattened, circular, green plate, as shown in 
fig. 156. It is attached near the center on one side to rushes 

i53 



154 



MORPHOLOGY. 



and other plants, and has been found quite abundantly for sev- 
eral years in the waters of Cayuga Lake at its southern extremity. 
As will be seen it consists of a single layer of green cells which 
radiate from the center in branched rows to the outside, the cells 
lying so close together as to form a continuous plate. The plant 
started its growth from a single cell at the central point, and grew 
at the margin in all directions. Sometimes they are quite irregu- 
lar in outline, when they lie quite closely side by side and inter- 
fere with one another by pressure. If the surface is examined 
carefully there will be found long hairs, the base of which is en- 
closed in a narrow sheath. It is from this character that the 
genus takes its name of coleochaete (sheathed hair). 

324. Fruiting stage of coleochaete. — It is possible at some 
seasons of the year to find rounded masses of cells situated near 
the margin of this green disk. These have developed from a 
fertilized egg which remained attached to the plant, and prob- 
ably by this time the parent plant has lost its color. 

325. Zoospore stage. — This mass of tissue does not develop 
directly into the circular green disk, but each of the cells forms 
a zoospore. Here then, as 
in cedogonium, we have an- 
other stage of the plant in- 
terpolated between the fer- 
tilized egg and that stage 
of the plant which bears the 
gametes. But in coleochaete 
we have a distinct advance in 
this stage upon what is pres- Fig- 157 . 
ent in cedogonium, for in , Portion of thaiius of a>- 

° ' leochaete scutata, showing 

coleochaete the fertilized empty . cells , from whic J h 

zoogonidia have escaped, 

egg develops first into a -jfaj.-jh^, .gg 

several -celled mass of tissue Prmgsheim.) 

before the zoospores are formed, while in cedogonium only four 

zoospores are formed directly from the egg. 

326. Asexual reproduction. — In asexual reproduction any of the green 
cells on the plant may form zoogonida. 




Fig. 158. 

Portion of thallus 
of Coleochaete 
scutata, showing 
four antheridia 
formed from one 
thallus cell ; a sin- 
gle spermatozoidat 
the right. (After 
Pringsheim.) 



The contents of a cell round off and 



COLEOCH^TE. 



155 



form a single zoogonidium which has two cilia at the smaller end of the oval 
body, fig. 157. After swimming around for a time they come to rest, ger- 
minate, and produce another plant. 

327. Sexual reproduction. — Oogonium. — The oogonium is formed by the 
enlargement of a cell at the end of one of the threads, and then the end of the 



Oo"g— 






Fig. 159. 

Coleochaete soluta ; at left branch bearing oogonium (oog); antheridia (nut); egg in 
oogonium and surrounded by enveloping threads ; at center three antheridia open, and one 
spermatozoid ; at right sporocarp, mature egg inside sporocarp wall. 

cell elongates into a slender tube which opens at the end to form a channel 

through which the spermatozoid may pass down to the egg. The egg is 

formed of the contents of the cell (fig. 159). Several oogonia are formed on 

one plant, and in such a 

IS55T 



plant as C. scutata they are 
formed in a ring near the 
margin of the disk. 

328. Antheridia.— In C. 
scutata certain of the cells 
of the plant divide into four 
smaller cells, and each one 
of these becomes an antheri- 
dium. In C. soluta the an- 




Fig. 160. 



Fig. 161. 
Two sporocarps still Sporocarp ruptured b y 
surrounded by thallus. growth of egg to form cell theridia grow out from the 
Thallus finally decavs and mass. Cells of this sporo- . . 

sets sporocarp free. phyte forming zoospores. end ol terminal cells in the 

F igs. 1 60, 161. C. scutata. form of short flasks, some- 

times four in number or less (fig. 159). A single spermatozoid is formed 
from the contents. It is oval and possesses two long cilia. After swim- 



15^ MORPHOLOGY. 

ming around it passes down the tube of the oogonium and fertilizes the 

e gg- 

329. Sporocarp. — After the egg is fertilized the cells of the threads near 
the egg grow up around it and form a firm covering one cell in thickness. 
This envelope becomes brown and hard, and serves to protect the egg. This 
is the "fruit" of the coleochsete, and is sometimes called a sporocarp 
(spore fruit). The development of the cell mass and the zoospores from the 
egg has been described above. 

Some of the species of coleochaete consist of branched threads, while others 
form circular cushions several layers in thickness. These forms together 
with the form of our plant C. scutata make an interesting series of transi- 
tional forms from filamentous structures to an expanded plant body formed 
of a mass of cells. 



COMPARISON OF ALGM. 



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CHAPTER XVIII. 

CLASSIFICATION AND ADDITIONAL STUDIES OF 
THE ALGyC. 

In order to show the general relationship of the algae studied, the princi- 
pal classes are here enumerated as well as some of the families. In some 
of the groups not represented by the examples studied above, a few species 
are described which may serve as the basis of additional studies if desired. 
The principal classes * of algae are as follows: 

Class Chlorophyceee. 

331. These are the green algae, so called because the chlorophyll green 
is usually not masked by other pigments, though in some forms it is. There 
are three subclasses. 

332. Subclass PROTOCOCCOIDE-ffi. — In the Protococcoideae are found the 
simplest green plants. Many of them consist of single cells which live an 
independent life. Others form "colonies," loose aggregations of individ- 
uals not yet having attained the permanency of even a simple plant body, 
for the cells often separate readily and are able to form new colonies. The 
colonies are often held together by a gelatinous membrane, or matrix. 
Some are motile, while others are non-motile. A few of the families are 
here enumerated. 

333. Family Volvocaceae. — These are all motile, during the vegetative 
stage. The individuals are single or form more or less globose colonies. 

334. The "red snow" plant (Sphaerella nivalis). — This is often found in 
arctic and alpine regions forming a red covering over more or less large 
areas of snow or ice. For this reason it is called the "red snow plant." 

335. Sphaerella lacustris, a closely related species, is very widely dis- 
tributed in temperate regions along streams or on the borders of lakes and 



* In Engler & Prantl's Pnanzenfamilien, Wille uses the term class for 
these principal subdivisions of the algae. Systomatists are not yet agreed 
upon a uniform use of the terms. 

158 



ALGJZ CONTINUED: CLASSIFICATION. 



159 



ponds. Here in dry weather it is often found closely adhering to the dry 
rock surface, and giving it a reddish color as if the rock were painted. This 
is especially the case in the shallow basins formed over the uneven surface 
of the rock near the water's edge. These places during heavy rains or in 
high water are provided with sufficient water to fill the basins. During 
such times the red snow plant grows and multiplies, loses its red color and 




.rig. 162. 
Sphaerella lacustris (Girod.) Wittrock. A, mature free-swimming individual 
with central red spot. B, division of mother individual to form two. C, divi- 
sion of a red one to form four. D, division into eight. E, a typical resting cell, 
red. F, same beginning to divide. G, one of four daughter zoospores after 
swimming around for a time, losing its red color and becoming green. (After 
Hazen.) 



becomes green, and, being motile, is free swimming. It is a single-celled 
plant, oval in form, surrounded by a gelatinous sheath and with two cilia 
or flagella at the smaller end, by the vibration of which it moves (fig. 162). 
The single cell multiplies by dividing into two cells. "When the water dries 
out of the basin, the motile plant comes to rest, and many of the cells assume 
the red color. To obtain the plant for study, scrape some of the red cov- 
ering from these rock basins and place it in fresh spring water, and in a day 
or so the swarmers are likely to be found. Under certain conditions small 
microzoids are formed. 

336. Chlamydomonas is a very interesting genus of motile one-celled 
green algae, because the species are closely related to the Flagellates among 
the lower animals. The plant is oval, with a single chloroplast and sur- 
rounded by a gelatinous envelope through which the two cilia or flagella 
extend. One-celled organisms of this kind are sometimes called monads, 
i.e., a one-celled being. This one has a gelatinous cloak and is, therefore, 
a cloaked monad {Chlamydomonas). The species often are found as a very 
thin green film on fresh water. C. pulvisculus is shown in fig. 163. "When 
it multiplies the single cell divides into two, as shown in B. Sometimes a 
non-motile palmella stage is formed, as shown in C and D. Reproduction, 



i6o 



MORPHOLOGY. 



takes place by gametes which are of unequal size, the smaller one repre- 
senting the sperm and the larger one the egg, as in E and F. These con- 




Fig. 163. 
Chlamydomonas pulvisculus (Mull.) Ehrb. A, an old motile individual; n, 
nucleus; p, pyrenoid; s, red eye spot; v, contractile vacuole; B, motile indi- 
vidual has drawn in its cilia and divided into two; C, mother plant has drawn 
in its cilia and divided into four non-motile cells; D, pamella stage; E, female 
gamete — egg; F, male gamete — sperm; G, early stage of conjugation; H, zygo- 
spore with conjugating tube and empty male cell attached. (After Wille.) 

jugate as in G and H, the protoplasm of the smaller one passing over into 
the larger one, and a zygospore is thus formed. 

337. Of those which form colonies, Pandorina morum is widely dis- 
tributed and not rare. It consists of a sphere formed of sixteen individuals 

enclosed in a thin gelatinous mem- 
brane. Each cell possesses two cilia 
(or flagella), which extend from the 
broader end out through the envelop- 
ing membrane. By the movement 
of these flagella the colony goes roll- 
ing around in the water. When the 
plant multiplies each individual cell 
divides into sixteen small cells, which 
then grow and form new colonies. 
Reproduction takes place when the 
individual cells of the young colonies 
separate, and usually a small indi- 
vidual unites with a larger one and 
a zygospore is formed (see fig. 164). 
Eudorina elegans is somewhat similar, 
but when the gametes are formed cer- 
tain mother cells divide into sixteen 
small motile males or sperms, and 
certain other mother cells divide into 
sixteen large motile females or eggs. 
These separate from the colonies, and 
the sperms pair with the eggs and fuse to form zygospores. This plant as 
well as Chlamydomonas pulvisculus foreshadows the early differentiation of 
sex in plants. 




Fig. 164. 
Pandorina morum (Mull.) Bory. I, 
motile colony; II, colony divided into 
16 daughter colonies; III, sexual colony, 
gametes escaping; IV, V, conjugating 
gametes; VI, VII, young and old zygo- 
spore; VIII. zygospore forming a large 
swarm spore, which is free in IX; X, 
same large swarm spore divided to form 
young colony. (After Pringsheim.) 



ALG& CONTINUED: CLASSIFICATION 



161 



338. Family Tetrasporaceae. — This family is well represented by Tetra- 
spora lubrica forming slimy green net-like sheets attached to objects in 
slow-running water. It is really a single-celled plant. The rounded cells 
divide by cross walls into four cells, and these again, and so on, large num- 
bers being held in loose sheets by the slime in which they are imbedded. 

339. Family Pleuroeoccaceae. — The members of this family are all non- 
motile in the vegetative stage. They consist of single individuals, or of 
colonies. Pleurococcus vulgaris (Protococcus vulgaris) 
is a single-celled alga, usually obtained with little difficulty. 
It is often found on the shaded, and cool, or moist side of 
trees, rocks, walls, etc., in damp places. This plant is 
not motile. It multiplies by fission (fig. 165) into two, 
then four, etc. These cells remain united for a time, then 
separate. Sometimes the cells are found growing out into 
filaments, and it is thought by some that P. vulgaris may 
be only a simple stage of a higher alga. Eremosphaera 
viridis is another single-celled alga found in fresh water 
among filamentous forms. The cells are large and globose. 

340. Family Hydrodictyaceae. — These plants form colonies of cells. 
Hydrodictyon reticulatum, the water net, is made up of large numbers of 
cylindrical cells so joined at their ends as to form a large open mesh or net. 
Pediastrum forms circular flat colonies, as shown in fig. 166. Both of these 




Fig. 165. 
Pleurococcus 
(protococcus) 
vulgaris. 




Fig. 166. 
Pediastrum boryanum. A, mature colony, most of the young colonies have 
escaped from their mother cells; at g, a young colony is escaping; sp, empty 
mother cells; B, young colony, C, same colony with spares arranged in order. 
(After Braun.) 

plants are rather common in fresh-water pools, the latter one intermingled 
with filamentous algae, while the former forms large sheets or nets. Mul- 
tiplication in Hydrodictyon takes place by the protoplasm in one of the cells 



1 62 



MORPHOLOGY. 



dividing into thousands of minute cells, which gradually arrange themselves 
in the form of a net, escape together from the mother cell, and grow into a 
large net. In Pediastrum multiplication takes place in a similar way, but 
the protoplasm in each cell usually divides into sixteen small cells, and 
escaping together from the mother cell arrange themselves and grow to full 
size (fig. 1 66). 

341. The Conjugates include several families of green algae, which prob- 
ably should be included among the Chlorophyceas. They have probably 
had their origin from some of the more simple members of the Protococ- 
coidese. They are represented by Spirogyra, Zygnema, and the desmids, 
studied in Chapter 14. 

342. Subclass CONFERVOIDEJE.— These are mostly filamentous algae, the 
filaments being composed of cells firmly united, and, with the exception of 
the simplest forms, there is a definite growing point. A few of the families 
are as follows: 

343. Family Ulvaceae. — These contain the sea wracks, or sea lettuce, 

like Ulva, forming expanded 
green, ribbon-like growths in the 
sea. 

344. Family Ulotrichaceae, 
represented by Ulothrix zonata, 
not uncommon in slow-running 
water or in ponds of fresh water 
attached to rocks or wood. It 
consists of simple threads of 
short cells. Multiplication takes 
place by zoospores. Repro- 
duction takes place by motile 
sexual cells (gametes) which 
fuse to form a zygospore (fig. 
167). 

345. Family Chaetophoraceae, 
germinating 'and represented by Chaetophora (in 




E 

Fig. 167. 
Ulothrix zonata. A, base of thread. B, 
cells with zoospores , C, one cell with zoospores 
escaping another cell with small biciliate 
gametes escaping and some fusing to form 
zygospores, E, zoospores 



spi 
forming threads: F £ zygospore growing and Chapter 15) and Drapernaudia 
forming zoospores. (After Caldwell and Dodel- r j/ r 

Port.) in fresh water. 

346. Family (Edogoniaceae, represented by (Edogonium (Chapter 16). 

347. Family Coleochaetaceae, represented by Coleochaete (Chapter 17). 

348. Subclass SIPHONED. — There are several families. 

349. Family Botrydiaceae. — This is represented by Botrydium granu- 
latum (Chapter 15, p. 146). 

350. Family Vaucheriaceae, represented by Vaucheria (Chapter 15), with 
quite a large number of species, is widely distributed. 



ALGM CONTINUED: CLASSIFICATION. 



163 




Class Schizophyceae (=Cyanophyceae). 

351. The Blue-Green Algae, or Cyanophyceae form slimy looking thin 
mats on damp wood or the ground, or floating mats or scum on the water. 
The color is usually bluish green, but in some species it is purple, red or 
brown. All have chlorophyll, but it is not in distinct chloroplasts and is 
more or less completely guised by the presence of other pigments. Two 
orders and eight families are recognized. The following include some of 
our common forms: 

352. ORDER COCCOGONALES (COCCOGONEJE).— Single-celled plants, 
occurring singly or in colonies, in some forms 
forming short threads. One of the two fami- 
lies is mentioned. 

353. Family Chroococcaceae. — The plants 
multiply only through cell division. Chroococ- 
cus, forms rounded, blue-green cells enclosed 
in a thick gelatinous coat, in fresh water and 
in damp places; certain species form "lichen- 
gonidia" in some genera of lichens. Gloeo- 
capsa is similar i;o Chroococcus, but the col- 
onies are surrounded by an additional common 
gelatinous envelope (fig. 168); on damp rocks, 
etc. 

354. ORDER HORMOGONALES (HORMOGONEJE).— Plants filamentous, 

^ simple celled or with false 

or true branching, usually 
several celled (Spirulina is 
single celled). Multiplica- 
tion takes place through 
hormogones, short sections 
of the threads becoming 
free; also through resting 
cells. Two of the six fami- 
lies are mentioned. 

355. Family Oscillatori- 
aceae. — This family is rep- 
resented by the genus Oscil- 
latoria, and by several other 
genera common and widely 
distributed. Oscillatoria 
contains many species. 
They are found on the 
damp ground or wood, or floating in mats in the water. They often form on 



Fig. 168. 
Gloeocapsa. 




Fig. 169. 
A, Oscillatoria princeps, a. terminal cell; b, c. 
portions from the middle of a filament. In c, a 
dead cell is shown between the living cells; B, 
Oscillatoria froelichii, b, with granules along the 
partition walls. 



164 



MORPtiOLOG Y. 



the soil at the bottom of the pool, and as gas becomes entangled in the mat 
of threads, it is lifted from the bottom and floated to the surface of the water. 
The plant is thread-like, and divided up into many short cells. The 
threads often show an oscillating movement, whence the name Oscillatoria. 
356. Family Nostocaceae.— This family is represented by Nostoc, which 
forms rounded, slimy, blue-green masses on 
wet rocks. The individual plants in the 
slimy ball resemble strings of beads, each 
cell being rounded, and several of these ar- 
ranged in chains as shown in fig. 170. Here 
and there are often found larger cells (hetero- 
cysts) in the chain. Nostoc punctiforme 
lives in the intercellular spaces of the roots 
of cycads (often found in greenhouses), and 
in the stems of Gunnera. N. sphaericum 
lives in the spaces between the cells in many 
species of liverworts (in the genera Antho- 
ceros, Blasia, Pellia, Aneura, Riccia, etc.), 
and in the perforated cells of Sphagnum 
acutifolium. Anabasna is another common 
and widely distributed genus. The species 
occur in fresh or salt water, singly or in slimy 
masses. Anabasna azqllae lives endophyti- 




Fig. 170. 
Nostoc linckii. A, filament 
with two heterocysts (h), and a 
large number of spores (sp)\ 
B, isolated spore beginning to cally in the leaves of the water fern, Azolla 
germinate; C, young filament 
developed from spore. (After 
Bornet.) 



Class Schizomycetes. 



357. Bacteriales. — The bacteria are sometimes classified with the Cyano- 
phyceae, under the name Schizophyta, and represent the subdivision Schiz- 
omycetes, or fission fungi, because 
many of them multiply by a divis- 
ion of the cells just as the blue -green 
algae do. For example, Bacillus 
forms rods which increase in length 
and divide into two rods, or it may 
grow into a long thread of many 

short rods. Micrococcus consists Fig. 171- 

r . , 1 i n r-, . Bacteria. A, Bacillus subtilis. Spores 

of Single rounded cells. Strepto- in threadSi unst ained rods, and stained rods 

coccus forms chains of rounded showing cilia; S Bacillus tetam, the teta- 
nus or lockjaw bacillus, found in garden 

cells, Sarcina forms irregular cubes soil and on old rusty nails. Spores in club- 

, j j ' ii i_m z-u Ti shaped ends. C, Micrococcus; D, Sarcina; 

of rounded cells, while others like £> streptococcus; F, Spirillum. (After 

Spirillum are spiral in form. Migula.) 

Bacillus subtilis may be obtained by making an infusion from hay and 





ALG^ CONTINUED: CLASSIFICATION. 1 65 

allowing it to stand for several days. Bacillus tetani occurs in the soil, on 
old rusty nails, etc. It is called the tetanus bacillus because it causes a 
permanent spasm of certain muscles, as in "lockjaw." This bacillus 
grows and produces this result on the muscles when it occurs in deep and 
closed wounds such as are caused by stepping on an old nail or other object 
which pierces the flesh deeply. In such a deep wound oxygen is deficient, 
and in this condition the bacillus is virulent. Opening the wounds to 
admit oxygen and washing them out with a solution of bichloride of mer- 
cury prevents the tetanus. Many bacteria are of great importance in bring- 
tttg about the decay of dead animal and plant matter, returning it to a con- 
dition for plant food. (See also nitrate and nitrite bacteria, Chapter IX.) 
While TtrOSt bacteria are harmless there are many which cause very serious 
diseases of t /ian and animals, as typhoid fever, diphtheria, tuberculosis, etc., 
while some others produce disease in plants. Others aid in certain fer- 
mentations 01 ]iquids and are employed for making certain kinds of wines 
or other beverages. Some work in symbiosis with yeasts, as in the kephir 
yeast, used in fermenting certain crude beverages by natives of some coun- 
tries. 

357a. MyxobacterialerS (Myxobacteriaoeae Thaxter *). — These plants con- 
sist of colonies of bacteria-like organisms, motile rods, which multiply by 
cross-division and secrete a gelatinous substance or matrix which surrounds 
the colonies. They form plasm odium-like masses which superficially 
resemble the slime moulds. In tfie fruiting stage some species become 
elevated from the substratum into cylindrical, clavate, or branched forms, 
which bear cysts of various shapes containing the rods in a resting stage, 
or the rods are converted into spore-like masses. Ex., Chondromyces 
crocatus on decaying plant parts, Myxobacter aureus on wet wood and 
bark, Myxococcus rubescens on dung, decaying lichens, paper, etc. 

Class Flagellata. 

358. The flagellates are organisms of very low organization resembling 
animals as much as they do plants. They are single celled and possess two 
cilia or flagella, by the vibration of which they move. Some are without a 
cell wall, while others have a well-defined membrane, but it rarely consists 
of cellulose. Some have chromatophores and are able to manufacture 
carbohydrates like ordinary green plants. These are green in Euglena, 
and brown in Hydrurus. Some possess a mouth-like opening and are able 
to injest solid particles of food (more like animals), while others have no 
such opening and absorb food substances dissolved in water (more like 
plants). The Euglena viridis is not uncommon in stagnant water, often 
forming a greenish film on the water. 

* See Bot, Gaz. ? 17, 389, 1892. 



i66 



MORPHOLOG Y. 



Class Peridineee. 

358a. These are peculiar one-celled organisms provided with two flagella 
and show some relationship to the Flagellates. They usually are provided 
with a cellulose membrane, which in some forms consists of curiously 
sculptured plates. In the higher forms this cellulose membrane consists of 
two valves fitting together in such a way as to resemble some of the diatoms. 
Like the Flagellates, some have green chromatophores, which in some are 
obscured by a yellow or brown pigment (resembling the diatoms), while 
still others have no chlorophyll. The Peridinese are abundant in the sea, 
while some are found in fresh water. 

Class Diatomaphyceae (Bacillariales, Diatomaceae). 

Zb%b. The diatoms are minute and peculiar organisms believed to be 
algae. They live in fresh, brackish, and salt water. They are often found 
covering the surface of rocks, sticks, or the soil in thin sheets. They occur 
singly and free, or several individuals may be joined into long threads, or 
other species may be attached to objects by slender gelatinous stalks. Each 

i k 




Fig. 171a. 
A group of Diatoms: c and d, top and side views of the same form; e, colony 
of stalked forms attached to an alga; f and g, top and side views of the form shown 
at e; h, a colony; i, a colony, the top and side view shown at k and n, forming auxo- 
spores. (After Kerner.) 

protoplast is enclosed in a silicified skeleton in the form of a box with two 
halves, often shaped like an old-fashioned pill box, one -half fitting over the 
other like the lid of a box. It is evident that in this condition the plant 
cannot increase much in size. 

They multiply by fission. This takes place longitudinally, i.e., in the 
direction of the two halves or valves of the box. Each new plant then has a 
valve only on one side. A new valve is now formed over the naked half, 
and fits inside the old valve. At each division the individuals thus become 
smaller and smaller until they reach a certain point, when the valves are 
cast off and the cell forms an auxospore, i.e., it grows alone, or after conju- 
gation with another, to the full size again, and eventually provides itself 



ALG& CONTINUED: CLASSIFICATION. 



167 



with new valves. The valves are often marked with numerous and fine 
lines, often making beautiful figures, and some are used for test objects for 
microscopes. 

The free forms are capable of movement. The movement takes place in 
the longitudinal direction of the valves. They glide for some time in one 
direction, and then stop and move back again. It is not a difficult thing to 
mount them in fresh water and observe this movement. 

The diatoms have small chlorophyll plates, but the green color is dis- 
guised by a brownish pigment called diatomin. The relationships of the 
diatoms are uncertain, but some, because of the color, think they are re- 
lated to the Phaeophyceae. 



Class Phaeophyceae. 

The brown algae. (Phaeophyceae). — The members of this class pos- 
sess chlorophyll, but it is obscured by a brown pig- 
ment. The plants are accessible at the seashore, 
and for inland laboratories may be preserved in 
formalin (2^ per cent). (See also Chapter LVI.) 

360. Ectocarpus. — The genus Ectocarpus repre- 
sents well some of the simpler forms of the brown 
algae (fig. 172). They are slender, filamentous 
branched algae growing in tufts, either epiphytic on 
other marine algae (oiten on Fucaceae), or on stones. 
The slender threads are o::ly divided crosswise, 
and thus consist of long series of short cells. The 
sporangia are usually plurilocular (sometimes uni- 





B 



Fig. 172. 
A, Ectocarpus siliculosus; B, branch with a young and a ripe 
plurilocular sporangium; E, gametes fusing to form zygospore. 
(B, after Thuret; E, after Berthold.) 



[68 



MORPHOLOGY. 




Fig. 173. 
Sphacelaria, portion 



algae 
giant 



locular), and usually occur in the place of lateral branches. The zoospores 
escape from the apex of the sporangium and are biciliate, and they fuse to 
form zygospores. 

361. Sphacelaria. — The species of this genus repre- 
sent an advance , in the development of the thallus. 
While they are filamentous and branched, division 
takes place longitudinally as well as crosswise (fig. 

173)- 

362. Leathesia difformis represents an interesting 
type because the plant body is small, globose, later 
irregular and hollow, and consists of short radiately 
arranged branches, the surface ones in the form of 
short, crowded, but free, trichome-like green branches. 

This trichothallic body recalls the similar form of 
of pfant" showing longi- Chsetophora pisiformis (Chapter 16) among the 
tudinal division of cells, rH,i nrrir> y lvr pfp 
and brood bud (pluri- ^nloropnycese. 

locular sporangium). 363. The Giant Kelps. — Among the brown 

are found the largest specimens, some of the laminarias or 
kelps, rivaling in size the largest land plants, 
and some of them have highly developed tissues. 
Postelsia palmceformis has a long, stout stem, from 
the free end of which extend numerous large and 
long blades, while the stem is attached to the rocks 
by numerous "root" like outgrowths, the holdfasts. 
It occurs along the northern Pacific coast, and 
appears to nourish where it receives the shock of 
the surf beating on the shore. Several species of 
Laminaria occur on our north Atlantic coast. In 
L. digitata, the stem expands at the end into a 
broad blade, which becomes split into several 
smaller blades (fig. 174). Macrocystis pyrijera 
inhabits the ocean in the southern hemisphere, and 
sometimes is found along the north American 
coast. It is said to reach a length of 200-300 
meters. 

364. Fucus, or Rockweed. — This plant is a more 
or less branched and flattened thallus or "frond." 
One of them, illustrated in fig. 119, measures 
15-30CW (6-12 inches) in length. It is attached to 
rocks and stones which are more or less exposed at low tide. From the base 
of the plant are developed several short and more or less branched expansions 
called "holdfasts," which, as their name implies, are organs of attachment. 
Some species (F. vesiculosus) have vesicular swellings in the thallu§, 




Fig. 174. 
Laminaria digitata, 
forma cloustoni, North 
Sea. (Reduced. 1 



A G^ CONTINUED: CLASSIFICATION. 



169 



The fruiting portions are somewhat thickened as shown in the figure. 
Within these portions are numerous oval cavities opening by a circular pore, 
which gives a punctate appearance to these fruiting cushions. Tufts of hairs 
frequently project through them. 

365. Structure of the concep'acles. — On making sections of the fruiting 
portions one finds the walls of the cavities covered with outgrowths. Some 
of these are short branches which bear a large rounded terminal sac, the 




Fig. 175- 
Portion of plant of Fucus show- 
ing conceptacles in enlarged ends; 
and below the vesicles (Fucus 
vesiculosus). 



Fig. 176. 
Section of conceptacle of Fucus, sho\ 
oogonia, and tufts of an.heridu. 



mg 



More slender and much- 
In these are developed 



oogonium, at maturity containing eight egg cells, 
branched threads bear narrowly oval antheridia 
several two-ciliated spermatozoidp. 

366. Fertilization, — At maturity the spermatozoids and egg cells float out- 
side of the oval cavities, where fertilization takes place. The spermatozojd. 



170 



MORPHOLOGY. 



sinks into the protoplasm of the egg cell, makes its way to the nucleus of 
the egg, and fuses with it as shown in fig. 181. The fertilized egg then 
grows into a new plant. Nearly all the brown algae are marine. 




Fig. 178. 
Antheridia of Fucus, on 
branched threads. 



Fig. 179. 
Antheridia of Fucus with 
escaping spermatozoids. 



Fig. 180. 
Eggs of Fucus surround- 
ed by spermatozoids. 







ass* 




. 



Fig. 181. 
Fertilization in Fucus; fn, female nucleus; mn, male nucleus; n, nucleolus. In 
the left figure the male nucleus is shown moving down through the cytoplasm of the 
egg; in the remaining figures the cytoplasm of the egg is omitted. (After Stras- 
burger.) * 

367. The Gulf weed (Sargassum bacciferum) in the warmer Atlantic 
ocean unites in great masses which float on the water, whence comes the 
name "Sargassum Sea." The Sargassum grows on the coast where it is 
attached to the rocks, but the beating of the waves breaks many specimens 
loose and these float out into the more quiet waters, where they continue 
to grow and multiply vegetatively. 

368. Uses. — Laminaria japonica and L. angustata are used as food by 
the Chinese and Japanese. Some species of the Laminariaceae are used as 
food for cattle and are also used for fertilizers, while L, digitata is some- 
times employed in surgery. 



ALG^ CONTINUED: CLASSIFICATION. 



17 



Classification. — Kjellman divides the Phaeophyceae into two orders. 

369. Order Phaeosporales (Phaeosporeae) including 18 families. One of 
the most conspicuous families is the Laminariaceae, including among others 
the Giant Kelps mentioned above (Laminaria, Postelsia, Microcystis, etc.). 

370. Order Cyclosporales (Cyclosporeae). — This include one family, the 
FucacecB with Ectocarpus, Sphacelaria, Laeathesia, Fucus, Sargassum, etc. 



Class Rhodophyceae. 

371. The red algae (Rhodophyceae). — The larger number of the so-called 
red alga? occur in salt water, though a few genera occur in fresh water. 
The plants possess chlorophyll, but it is usually obscured by a reddish or 
purple pigment. 

372. Nemalion. — This is one of the lower marine forms, though its thal- 
lus is not one of the simplest in struc- 
ture. The plant body consists of a 
slender cylindrical branched shoot, some- 
times very profusely branched. The 
central strand is rather firm, while the 
cortex is composed of rather loose fila- 
ments. 

373. Batrachospermum. — This genus 
occurs in fresh water, and the species 
are found in slow-running water of 
shallow streams or ditches. There is a 
central slender strand which is more or 
less branched, and on these branches 
are whorls of densely crowded slender 
branches occurring at regular intervals. 
The plants are usually very slippery. 
Gonidia are formed on the ends of some 
of these branches in globose, sporangia, 
called monosporangia, since but a single 




Fig. 182. 



A red alga (Nemalion). ^.sexual 

spore or gonidium is developed in each, branches, showing antheridia (a); 

Other branches often terminate in long carpogonium or procarp (0) with its 

o tnchogyne (/), to which are attached 

slender hyaline setae. two spermatia (s)\ B, beginning of 

*iiA Ta»v,o„,>o '-T-,- , a cystocarp (0), the trichogvne (/) 

374. Lemanea.— This genus also occurs still showing; C, an almost mature 

in fresh water. The species develop S^^&^tervgelT 12 ^ 
only during the cold winter months in 

rapids of streams or where the water from falls strikes the rocks and is 
thoroughly aerated. They form tufts of greenish threads, cylindrical or 
whiplike, which in the summer are usually much broken down. The 
threads are hollow and have a firm cortex. These are the sexual shoots, 



172 



MORPHOLOGY. 



and they arise as branches from a sterile filamentous-branched, Chantransia- 
like form. 

375. Fertilization in the lower red algae. — The sexual organs in the red 
algas consist of antheridia and carpogonia. The antheridia are usually 
borne in crowded clusters, or surfaces, and bear terminally the small non- 
motile sperm cells. The carpogonium is a branch of one or several cells, 
the terminal cell (procarp) extending into a long slender process, the tri_ 
chogyne. The sperm cell comes in contact with the trichogyne, and in the 
case of Nemalion and some others the nucleus has been found to pass down 
the inside and fuse with the nucleus of the procarp. 

From this point in the lower red algas like Nemalion, Batrachospermum 




Fig. 183. 
A, part of a shoot showing whorls of branches with clusters of carpospores. 
B, carpogonic branch or procarp. c, procarp cell; tr, trichogyne. C. same with 
sperm (sp) uniting with trichogyne. D, same with carpospores developing from 
procarp cell. E, male branch with one-celled antheridia. F, same with some of 
antheridia empty. ( After Schmitz. ) 

and Lemanea the formation of the spores is very simple. The procarp is 
stimulated to growth, and buds in different directions, producing branched 
chains of spores (carpospores). The carpospores form a rather compact 



A t G& CON TIN UED : CLA SSlFl CA T10N. 



173 



cluster called the sporocarp, which means spore-fruit or spore-fruit body. 
In Batrachospermum it is seen as a compact tuft in the loose branching, in 
Nemalion it lies in the surface of the cortex, while in Lemanea the sporo- 
carps lie at different positions in the hollow tube of the sexual shoot. 

376. Gonidia in the red algae. — The common type of gonidium in the red 
algae is found in the tetraspores. A single mother cell divides into four cells 
arranged usually in the form of tetrads within the tetrasporangium. In 
Callithamnion the tetrasporangium is exposed. In Polysiphonia, Rhab- 




Fig. 184. 

A red alga (Callithamnion), showing spor- 
angium A, and the tetraspores discharged 
B. (After Thuret.) 




Fig. 185. 
Gracilana, portion of frond, 
showing position of cystocarps. 



Fig. 186. 
Gracilaria, section of cysto- 
carp showing spores. 



donia, Gracilaria, etc., it is imbedded in the cortex. In Batrachosper 
there are monosporangia, each monosporangium containing a singk 
dium, while in Lemanea, and according to some also in Nemalion, 
are wanting. 



174 



MORPHOLOGY. 



377. Gracilaria. — Gracilaria is one of the marine forms, and one species 
is illustrated in fig. 185. It measures 15-20CW or more long, and is pro- 
fusely branched in a palmate manner. The parts of the thallus are more 
or less flattened. The fruit is a cystocarp, which is characteristic of the 
Rhodophyceae (Florideae). In Gracilaria these fruit bodies occur scat- 
tered over the thallus. They are somewhat flask -shaped, are partly sunk 
in the thallus, and the umical end projects strongly above the surface. The 
carpospores are grouped in radiating threads within the oval cavity of the 
cystocarp. These cystocarps are developed as a result of fertilization. 
Other plants bear gonidia in groups of four, the so-called tetraspores. 

378. Rhabdonia. — This plant is about the same size as the gracilaria, 
though it possesses more filiform branches. The cystocarps form prom- 
inent elevations, while the carpospores lie in separated groups around the 




Fig. 187. 
Rhabdonia, branched 
portion of frond show- 
ing cystocarps. 




Fig. iJ 

Section of cystocarp of rhabdonia, showing 
spores. 



periphery of a sterile tissue within the cavity. (See figs. 187, 188.) Goni- 
dia in the form of tetraspores are also developed in Rhabdonia. 

379. Fertilization of the higher red algae. — The process of fertilization in 
most of the red algae is very complicated, chiefly because the fertilized egg 
cell (procarp) does not develop the spores directly, as in Nemalion, Le- 



ALG^E CONTINUED: CLASSIFICATION. 



175 



let 



manea, etc., tut fuses directly, or by a short cell or long filament with one 
or more auxiliary cells before the sporocarp is finally formed. Examples 
are Rhabdonia, Polysiphonia, 
Callithamnion, Dudresnaya, 
etc. (fig. 189). The auxiliary 
cell then develops the sporo- 
carp. See fig. 189 for conju- 
gation of a filament from the 
fertilized procarp with an aux- 
iliary cell. 

380. Uses of the red algae. — 
Many species produce a great 
amount of gelatinous sub- 
stance in their tissues, and 
several of these are used for 
food, for the manufacture of 
gelatines and agar-agar. Some 
of these are Gracilaria lich- 
enoides and wrightii, the for- 
mer species occurring along 
the coast of India and China. 
The plant is easily converted 
into gelatinous substance 
(agar-agar). Chondrus cris- 
pus, widely distributed in the 
northern Atlantic is known as 
u Irish" moss and is used for food and for certain medicinal purposes. 
Gigartina mamillosa in the Atlantic and Arctic oceans is similarly em- 
ployed. The following orders are recognized in the red algae: 

381. Order Bangiales. — Example, Bangia atropurpurea (= Conferva 
atropurpurea) in springs and brooks in North America and Europe. Por- 
phyra contains a number of species forming broad, thin, leaf-like purple 
sheets in the sea. 

382. Order Nemalionales. — Including Lemanea, Batrachospermum, 
Nemalion, described above, and many others. 

383. Order Gigartinales. — In this order occurs the common Iceland 
moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina men- 
tioned above. 

384. Order Rhodomeniales. — In this order occurs Gracilaria and Poly- 
siphonia mentioned above, also the beautiful marine forms like Ceramium. 

385. Order Cryptonemiales. — Examples are Dudresnaya, Melobesia, 
Corallina, etc., the last two genem include many species with a wide dis- 
tribution. 




tr, trichogyne, with 
ct, connecting-tube 



Fig. 
Dudresnaya purpurifera. 
spermatozoids attached : 

which grows out from below the base of the 
trichogyne, and comes in contact with the fertile 
branches f, f\ct', young connecting-tube. (After 
Thuret and Bornet.) 



176 



MORPHOLOGY. 



Class Charophyceae, Order Charales. 

386. The Charales are by some thought to represent a distinct class of 
clgae standing near the mosses, perhaps, because of the biciliate character of 
the spermatozoids. There is one family, the Characese. The plants occur 
in fresh and brackish water. Aside from the peculiarity of the reproductive 
organs they are remarkable for the large size of the cells of the internodes 
and of the "leaves," and the protoplasm exhibits to a remarkable degree 

the phenomenon of "cyclosis" 
(see paragraphs 17-20). Three 
of the genera are found in North 
America (Chara, Nitella (Fig. 8) 
and Tolypella). 

386a. The complicated struc- 
ture of the sexual organs shows a 
higher state of organization than 
any of the other living algae 
known. While the internodes in 
Nitella are composed of a single, 
stout cell, some times a foot or 
more in length, the nodes in all are 
composed of a group of smaller 
cells. From the lateral cells of 
this group lateral axes (sometimes 
called leaves) arise in whorls. 
In Nitella the internodes are 
dium, a, and a carpogonium, s, surrounded na v e d v ut ; n most o^pipo n f 
by the spirally twisted enveloping cells; c, naKea > Dut m most species Ot 
crown of five cells at apex; /?, sterile lateral Chara they are corticated, i.e., they 
leaflets; /?', large lateral leaflet near the fruit; , , , . 

/?", bracteoles springing from the basal node are covered by a layer of numer- 
of the reproductive organs. B, a young elnncrpterl relk whirh arnw 

antheridium, a, and a young carpogonium, OUS elongated cells wnicn grow 
sk; w, nodal cell of leaf; u, intermediate downward from the nodes at the 
cell between w and the basal -node cell of 

the antheridium; /, cavity of the internode base of the whorl of lateral shoots, 
of the leaf; br, cortical cells of the leaf. oo fih T i QPYlia i nTO!in( . nr ~ 
AX about 33; 5X240. (After Sachs.) tf8bD ' lhe sexual organs are 

situated at the nodes of the 
whorled lateral shoots, and consist of antheridia and carpogonia. Most of 
the plants are monoecious, and both antheridia and carpogonia are often 
attached to the same node, the antheridium projecting downward while the 
carpogonium is more or less ascending. The sexual organs are visible 
to the unaided eye. The antheridium is a globose red body of an exceed- 
ingly complicated structure. The sperms are borne in several very long 
coiled slender threads which are divided transversely into numerous cells. 
The carpogonium is oval or elliptical in outline, the wall of which is com- 
posed of several closely coiled spiral threads enclosing the large egg. 




Fig. 172a. 
Reproductive organs of Chara fragilis. 
a central portion of a leaf, b, with an anther- 



CHAPTER XIX. 

FUNGI : MUCOR AND SAPROLEGNIA. 

Mucor. 

387. In the chapter on growth, and in our study of proto- 
plasm, we have become familiar with the vegetative condition of 
mucor. We now wish to learn how the plant multiplies and re- 
produces itself. For this study we may take one of the mucors. 
Any one of several species will answer. This plant may be grown 
by placing partially decayed fruits, lemons, or oranges, from which 
the greater part of the juice has been removed, in a moist cham- 
ber • or often it occurs on animal excrement when placed under 
similar conditions. In growing the mucor in this way we are 
likely to obtain Mucor mucedo, or another plant sometimes 
known as Mucor stolonifer, or Rhizopus nigricans, which is illus- 
trated in fig. 191. This latter one is sometimes very injurious to 
stored fruits or vegetables, especially sweet potatoes or rutaba- 
gas. Fig. 190 is from a photograph of this fungus on a banana. 

388. Asexual reproduction. — On the decaying surface of the 
vegetable matter where the mucor is growing there will be seen 
numerous small rounded bodies borne on very slender stalks. 
These heads contain the gonidia, and if we sow some of them in 
nutrient gelatine or agar in a Petrie dish the material can be 
taken out very readily for examination under the microscope. 
Or we may place glass slips close to the growing fungus in the 
moist chamber, so that the fungus will develop on them, though 
cultures in a nutrient medium are much better. Or we may take 
the material directly from the substance on which it is growing. 

177 



i;8 



MORPHOLOG Y. 



After mounting a small quantity of the mycelium bearing these 
heads, if we have been careful to take it where the heads appear 
quite young, it may be possible to study the early stages of their 




Fig, 190, 
Portion of banana with a mould (Rhizopus nigricans) growing on one end. 

development. We shall probably note at once that the stalks or 
upright threads which support the heads are stouter than the 
threads of the mycelium. 

These upright threads soon have formed near the end a cross 
wall which separates the protoplasm in the end from the remain- 
der. This end cell now enlarges into a vesicle of considerable 
size, the head as it appears, but to which is applied the name of 
sporangium (sometimes called gonidangium), because it encloses 
the gonidia. 

At the same time that this end cell is enlarging the cross wall 
is arching up into the interior. This forms the columella. All 
the protoplasm in the sporangium now divides into gonidia. 
These are small rounded or oval bodies. The wall of the spo- 



FUNGI: MUCOR. 1^9 

rangium becomes dissolved, except a small collar around the 
stalk which remains attached below the columella (fig. 192). 




Fig. 191. 

> nigricans 

ing from an older group. 



Group of sporangia of a mucor (Rhizopus nigricans) showing rhizoids and the stolon extend- 
frc 



By this means the gonidia are freed. These gonidia germinate 
and produce the mycelium again. 

389. Sexual stage. — This stage is not so frequently found, but may some- 
times be obtained by growing the fungus on bread. 

Conjugation takes place in this way. Two threads of the mycelium which 
lie near each other put out each a short branch which is clavate in form. 
The ends of these branches meet, and in each a septum is formed which cuts 
off a portion of the protoplasm in the end from that of the rest of the my- 
celium. The meeting walls of the branches now dissolve and the protoplasm 
of each gamete fuses into one mass. A thick wall is now formed around this 
mass, and the outer layer becomes rough and brown. This is the zygote or 
zygospore. The mycelium dies and it becomes free often with the suspensors, 
as the stalks of these sexual branches are called, still attached. This zygo- 
spore passes through a period of rest, when with the entrance of favorable 
conditions of growth it germinates, and usually produces directly a sporan- 
gium with gonidia. This completes the normal life cycle of the plant. 

390. Gemmae. — Gemmae, as they are sometimes called, are often formed on 
the mycelium. A short cell with a stout wall is formed on the side of a 



l80 MORPHOLOGY. 

thread of the mycelium. In other cases large portions of the threads of the 
mycelium may separate into chains of cells. Both these kinds of cells are 





Fig. 194. 
A mucor (Rhizopus nigricans) ; at left nearly mature sporangium with columella showing 
within; in the middle is ruptured sporangium with some of the gonidia clinging to the colu- 
mella ; at right two ruptured sporangia with everted columella. 

capable of growing and forming the mycelium again. They are sometimes 
called chlamydosporcs. 

390a. The Mucorineae according to their manner of zygospore formation 
are of two kinds: 1st, the homothallic (monoecious), in which all of the colo- 
nies 01 thalli developed from different spores are the same, and both gametes 
may be developed from the mycelium from a single spore, as in Sporodinia 
grandis, a mould common on old mushrooms; 2d, the heterothallic (dioe- 
cious), in which certain plants are of a male nature and small in compari- 
son with those of perhaps a female nature which are larger or more vigor- 
ous. When grown separately each of these two kinds of thalli, or colonies 
of mycelium, produce their own kind but only sporangia. If the two kinds 
are brought together, however, branches from one conjugate with branches 
from the other and zygospores are produced, as in Rhizopus nigricans, the 
common bread or fruit mould. This is one reason why we rarely find this 
fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the 
Mucorineae, Proc. Am. Acad. Arts and Sci., 40, 205-319, pi. 1-4, i9°4-) 



FUNGI: SAPROLEGNIA. 



181 



Water Moulds (Saprolegnia). 

391. The water moulds are very interesting plants to study 
because they are so easy to obtain, and it is so easy to observe a 
type of gonidium here to which we have referred in our studies 
of the algae, the motile gonidium, or zoogonidium. (See appen- 
dix for directions for cultivating this mould.) 

392. Appearance of the saprolegnia. — In the course of a 
few days we are quite certain to see in some of the cultures deli- 
cate whitish threads, radiating outward from the body of the fly 
in the water. A few threads should be examined from day to 
day to determine the stage of the fungus. 

393. Sporangia of saprolegnia. — The sporangia of saprolegnia 
can be easily detected because they are much stouter than the 
ordinary threads of the mycelium. Some of the threads should 
be mounted in fresh water. Search for some of those which 




Fig. 195- 
of saprolegnia, one showing the escape of the zoogo- 
nidia., 

show that the protoplasm is divided up into a 
great number of small areas, as shown in fig. 195. 
With the low power we should watch some of the older ap- 
pearing ones, and if after a few minutes they do not open, other 
preparations should be made. 



1 82 MORPHOLOGY. 

391. Zoogonidia of saprolegnia. — The sporangium opens at 




Fig. iq6. 
Branch of saprolegnia showing oogonia with oospores, eggs matured parthenogenetically. 

the end, and the zoogonidia swirl out and swim around for a 
short time, when they come to rest. With a good magnifying 




Fig. 197- 
Downy mildew of grape (Plasmopora viti- 
cola), showing tuft of gonidiophores bearing 
gonidia, also intercellular mycelium. (After 
Millardet.) 



Fig. 198. 
Phytophthora infestans showing pe- 
culiar branches ; gonidia below. 



power the two cilia on the end may be seen, or we may make 



FUNGI: SAPROLEGNIA. 



IS3 





Fig. 199. 
Fertilization in saprolegnia, tube of antheridium carrying in the nucleus of the sperm cell 
to the egg. In the right-hand figure a smaller sperm nucleus is about to fuse with the 
nucleus of the egg. (After Humphrey and Trow.) 





Fig. 200. 
Branching hypha of Peronospora alsinearum. 



Fig. 20 1. 
Branched hypha of downy mildew 
of grape showing peculiar branching 
(Plasmopara viticola). 



1 84 



MORPHOLOGY. 



them more distinct by treatment with Schultz's solution, draw- 
ing some under the cover glass. The zoogonidium is oval and 
the cilia are at the pointed end. After they have been at rest 
for some time they often slip out of the thin wall, and swim 
again, this time with the two cilia on the side, and then the 
zoogonidium is this time more or less bean-shaped or reniform. 

395. Sexual reproduction of saprolegnia. — When such cultures are older 
we often see large rounded bodies either at the end of a thread, or of a 
branch, which contain several smaller rounded bodies as shown in fig. 196. 
These are the oogonia (unless the plant is attacked by a parasite), and the 
round bodies inside are the egg cells, if before fertilization, or the eggs, if 
after this process has taken place. Sometimes the slender antheridium can 
be seen coiled partly around the oogonium, and one end entering to come in 
contact with the egg cell. But in some species the antheridium is not 
present, and that is the case with the species figured at 196. In this case 




Fig. 202. Fig. 203. 

Gonidiophores and gonidia of potato blight (Phytophthora in- Gonidia of potato 

festans). b, an older stage showing how the branch enlarges where blight forming zoogo- 

it grows beyond the older gonidium. (After de Bary.) nidia. (After de Bary.) 

the eggs mature without fertilization. This maturity of the egg without 
fertilization is called parthenogenesis, which occurs in other plants also, but 
is a rather rare phenomenon. 

396. In fig. 199 is shown the oogonium and an antheridium, and the 
antheridium is carrying in the male nucleus to the egg cell. Spermatozoids 
are not developed here, but a nucleus in the antheridium reaches the egg 
cell. It sinks in the protoplasm of the egg, comes in contact with the nu- 
cleus of the egg, and fuses with it. Thus fertilization is accomplished. 



FUNGI: DOWNY MILDEWS. 



I8 5 



Downy Mildews. 

397. The downy mildews make up a group of plants which are closely 
related to the water moulds, but they are parasitic on land plants, and some 
species produce very serious diseases. The mvcelium grows between the 




Fig. 204. 
Fertilization in Peronospora alsinearum; tube from antheridium carrying in the 
sperm nucleus in figure at the left, female nucleus near; fusion of the two nuclei 
shown in the two other figures. (After Berlese.) 



cells of the leaves, stems, etc., of their hosts, and sends haustoria into the 
cells to take up nutriment. Gonidia are formed on threads which grow 
through the stomates to the out- 
side and branch as shown in figs. 
198-201 . The gonidia are borne 
on the tips of the branches. The 
kind of branching bears some re- 
lation to the different genera. 
Fig. 200 is from Peronospora 
alsinearum on leaves of ceras- 
tium; figs. 197 and 199 are Plas- 
mopara viticola, the grape mil- 
dew, while figs. 198 and 202 are 
from Phytophthora infestans 
which causes a disease known as 
potato blight. The gonidia of 
peronospora germinate by a germ 
tube, those of plasmopara first 
form zoogonidia, while in phy- 
tophthora the gonidium may either germinate forming a thread, or each 
gonidium may first form several zoogonidia, as shown in fig. 20 v 

398. In sexual reproduction oogonia and antheridia are developed on the 
mycelium within the tissues. Fig. 204 represents the antheridium enter- 




Fig. 205. 
Ripe oospore of Peronospora alsinearum. 



1 86 MORPHOLOG Y. 

ing the oogonium, and the male nucleus fusing with the female nucleus 
in fertilization. The sexual organs of Phytophthora infestans are not 
sufficiently known. 

399. Mucor, saprolegnia, peronospora, and their relatives have few or 
no septa in the mycelium. In this respect they resemble certain of the algae 
like vaucheria, but they lack chlorophyll. They are sometimes called the 
alga-like fungi and belong to a large group called Phycomycetes. 



CHAPTER XX. 



FUNGI CONTINUED. 



Rusts" (Uredineae). 



400. The fungi known as "rusts" are very important ones 
to study, since all the species are parasitic, and many produce 
serious injuries to crops. 

401. Wheat rust (Puccinia graminis). — The wheat rust is 
one of the best known of these fungi, since a great deal of study 
has been given to it. One form of the plant occurs in long 



m 






Fig. 206. 
Wheat leaf with red 
rust, natural size. 



Fig. 207. Fig. 208. Fig. 209. Fig. 2 to. 

Portion of eaf Natural size. Enlarged. Single 

darged to show sorus. 



Figs. 206, 207. — Puccinia graminis, red-rust stage (uredo stage). 
Figs. 208-210. — Black rust of wheat, showing sori of teleutospores. 

reddish-brown or reddish pustules, and is known as the "red 
rust" (figs. 206, 207). Another form occurs in elongated black 
pustules, and this form is the one known as the "black rust" 

187 



1 88 



MOKPHOLOG Y. 



(figs. 208-211). These two forms occur on the stems, blades, 
etc., of the wheat, also on oats, rye, and some of the grasses. 

402. Teleutospores of the black-rust form. — If we scrape off 
some portion of one of the black pustules (sori), tease it out 





Fig. 212. 

Teleutospores of wheat rust, 

showing two cells and the pedicel. 




Fig. 211. 
Head of wheat showing black rust spots 
on the chaff and awns. 



Fig. 213. 
Uredospores of wheat rust, one 
showing remnants of the pedicel. 



in water on a slide, and examine with a microscope, we see 
numerous gonidia, composed of two cells, and having thick, 
brownish walls as shown in fig. 212. Usually there is a slender 
brownish stalk on one end. These gonidia are called teleuto- 
spores. They are somewhat oblong or elliptical, a little con- 
stricted where the septum separates the two cells, and the end 
cell varies from ovate to rounded. The mycelium of the fungus 



FUNGI: RUSTS. 



189 



courses between the cells, just as is found in the case of the 
carnation rust, which belongs to the same family (see Parag. 186). 
403. Uredospores of the red-rust form. — If we make a simi- 
lar preparation from the pustules of the red-rust form we see 
that instead of two-celled gonidia they are one-celled. The 
walls are thinner and not so dark in color, and they are covered 
with minute spines. They have also short stalks, but these fall 
away very easily. These one-celled gonidia of the red-rust form 
are called "uredospores." The uredospores and teleutospores 
are sometimes found in the same pustule. 

It was once supposed that these two kinds of gonidia belonged 
to different p ] ants, but now it is known that the one-celled 
form, the uredospores, is a form developed 
earlier in the season than the teleutospores. 
404. Cluster-cup form on the barberry. 
— On the barberry is found still another 
form of the wheat rust, the ' ' cluster cup ' ' 
stage. The pustules on the under side of 
the barberry leaf are cup-shaped, the cups 
being partly sunk in the tissue of the leaf, 
while the rim is more or less curved back- 
ward against 
the leaf, and 
split at several 
places. These 
cups occur in 
clusters on the 
affected spots 
of the barberry 
leaf as shown 

Two cluster \\\ fi£f. 2 IS. 
cups more en- J 

larged, showing Within the 

split margin. 
Figs. 214-21 6.— Cluster-cup stage of wheat rust. CUpS numbers 

of one-celled gonidia (orange in color, called secidios pores) are 
borne in chains from short branches of the mycelium, which 
fill the base of the cup. In fact the wall of the cup (peridium) 






Fig. 214. 
Barberry leat with two 
diseased spots, natural 
size. 



Fig. 215. 
Single spot 
showing cluster 
cups enlarged. 



190 



MORPHOLOG Y. 



is formed of similar rows of cells, which, instead of separating 
into gonidia, remain united to form a wall. These cups are 
usually borne on the under side of the leaf. 

405. Spermagonia. — Upon the upper side of the leaves in the same spot 
occur small, orange-colored pustules which are flask-shaped. They bear 
inside, minute, rod-like bodies on the ends of slender threads, which ooze 




Fig. 217. 
Section of an aecidium (cluster cup) from barberry leaf. 



(After Marshall-Ward.) 



out on the surface of the leaf. These flask-shaped pustules are called 
spermagonia, and the minute bodies within them spermatia, since they were 
once supposed to be the male element of the fungus. Their function is not 
known. They appear in the spots at an earlier time than the cluster cups. 

406. How the cluster-cup stage was found to be a part of the wheat rust. 
— The cluster-cup stage of the wheat rust was once supposed also to be a dif- 
ferent plant, and the genus was called cecidium. The occurrence of wheat 
rust in great abundance on the leeward side of affected barberry bushes in 
England suggested to the farmers that wheat rust was caused by barberry 
rust. It was later found that the secidiospores of the barberry, when sown 
on wheat, germinate and the thread of mycelium enters the tissues of the 
wheat, forming mycelium between the cells. This mycelium then bears 
the uredospores, and later the teleutospores. 



FUNGI: RUSTS, 



19] 



407. Uredospores can produce successive crops of uredospores. — The uredo- 
spores are carried by the wind to other wheat or grass plants, germinate 




Fig. 218. 
Section through leaf of barberry at point affected with the cluster-cup stage of the wheal 
rust; spermagonia above, ascidia below. (After Marshall-Ward.) 

form mycelium in the tissues, and later the pustules with a second crop oi 
uredospores. Several successive crops of uredospores may be developed in 





Fig. 219. 
A, .section through sorus of black rust of wheat, showing teleutospores. B, nvycelium 
bearing both teleutospores and uredospores. (After de Bary.) 

one season, so this is the form in which the fungus is greatly multiplied and 
widely distributed. 



192 



MORPHOLOGY. 



407a. Teleutcspores the last stage of the fungus in the season. — The teleu- 

tospores are developed late in the season, or late in the development of the 

host plant (in this case the 
wheat is the host). They 
then rest during the winter. 
In the spring under favor- 
able conditions each cell of 
the teleutospore germi- 
nates, producing a short 
mycelium called a promy- 
celium, as shown in figs. 
222, 223. This promy- 
celium is usually divided 
into four cells. From each 
cell a short, pointed pro- 
cess is formed called a 
<l sterigma." Through this 
the protoplasm moves and 
forms a small gonidium on 
the end, sometimes called 
a sporidium. 
408. How the fungus gets from the wheat hack to the harherry. — If these 

sporidia from the teleutospores are carried by the wind so that they lodge on 




20. Fig. 221. 

Germinating uredospore of Germ tube entering the 

wheat rust. (After Marshall- leaf through a stoma. 
Ward.) 




Fig. 222. 
Teleutospore germi- 
nating, forming pro my- 
celium. 

Figs. 222-224. — 



Fig. 223. 
Pro mycelium of ger- 
minating teleutospore, 
forming sporidia. 
Puccinia graminis (wheat rust) 



Germinating sporidia entering leaf 
of barberry by mycelium. 

(After Marshall-Ward.) 



FUNGI: RUSTS. 193 

the leaves of the barberry, they germinate and produce the cluster cup again. 
The plant has thus a very complex life history. Because of the presence of 
several different forms in the life cyle, it is called a polymorphic fungus. 

The presence of the barberry does not seem necessary in all cases for the 
development of the fungus from one year to another. 

409. Synopsis of life history of wheat rust. 

Cluster -cup stage on leaf of barberry. 

Mycelium between cells of leaf in affected spots. 
Spermagonia (sing, spermagonium), small flask-shaped bodies 

sunk in upper side of leaf; contain " spermatia." 
^Ecidia (sing, aecidium), cup-shaped bodies in under side of 
leaf. 
Wall or peridium, made up of outer layer of fungus threads 

which are divided into short cells but remain united. 
At maturity bursts through epidermis of leaf; margin of 
cup curves outward and downward toward surface of leaf. 
Central threads of the bundle are closely packed, but free. 
Threads divide into short angular cells which separate 
and become secidiospores, with orange-colored content. 
^Ecidiospores carried by the wind to wheat, oats, grasses, 
etc. Here they germinate, mycelium enters at stomate, 
and forms mycelium between cells of the host. 

Uredo stage {red rust) on wheal, oats, grasses, etc. 
Mycelium between cells of host. 
Bears uredospores (i -celled) in masses under epidermis, which 

is later ruptured and uredospores set free. 
Uredospores carried by wind to other individual hosts, and 

new crops of uredospores formed. 

Teleutospore stage {black rust), also on wheal, etc. 

Mycelium between cells of host. 

Bears teleutospores (2 -celled) in masses (sori) under epidermis, 
which is later ruptured. 

Teleutospores rest during winter. In spring each cell germi- 
nates and produces a promycelium, a short thread, divided 
into four cells. 



1 94 MORPHOL OGY. 

Promycelium bears four sterigmata and four gonidia (or spo- 
ridia), which in favorable conditions pass back to the bar- 
berry, germinate, the tube enters between cells into the 
intercellular spaces of the host to produce the cluster cup 
again, and thus the life cycle is completed. 

410. Other examples of the rusts. — Some of the rusts do great injury to 
fruit trees and also to forest trees. The "cedar apples" are abnormal 
growths on the leaves and twigs of the cedar stimulated by the presence of 
the mycelium of a rust known as Gymnosporangium macropus. The 
teleutospores are two celled and are formed in the tissue of the "cedar 
apple" or gall. The teleutosori are situated at quite regular intervals over 
the surface of the gall at small circular depressions, and can be easily seen 
in late autumn and during the winter. A quantity of gelatine is developed 
along with the teleutospores. In early spring with the warm spring rains 
the gelatinous substance accompanying the teleutospores swells greatly, and 
causes the teleutospores to ooze out in long, dull, orange-colored strings, 
which taper gradually to a slender point and bristle all over the "cedar 
apple." Here the teleutospores germinate and produce the sporidia. The 
sporidia are carried to apple trees where they infect leaves and even the 
fruit, producing here the cluster cups. There are no uredospores. 

G. globosum is another species forming cedar apples, but the gelatinous 
strings of teleutospores are short and clavate, and the cluster cups are 
formed on hawthorns. G. nidusavis forms "witches brooms" or "birds 
nests ' ' in the branches of the cedar. The mycelium in the branches stimu- 
lates them to profuse branching so that numerous small branches are devel- 
oped close together. The teleutosori form small pustules scattered over the 
branches. G. clavipes affects the branches of cedar only slightly deform- 
ing them or not at all, and the cluster cups are formed en fruits, twigs, and 
leaves of the hawthorns or quinces, the cluster cups being long, tubular, 
and orange in color. 



CHAPTER XXI. 

THE HIGHER FUNGI. 

411. The series of the higher fungi. — Of these there are two 
large series. One of these is represented by the sac fungi, and 
the other by the mushrooms, a good example of which is the 
common mushroom (Agaricus campestris). 

Sac Fungi (Ascomycetes). 

412. The sac fungi may be represented by the " powdery mil- 
dews"; examples, uncinula, microsphgera, podosphaera, etc. 
Fig. 225 is from a photograph of two willow leaves affected by 
one of these mildews. The leaves are first partly covered with a 
whitish growth of mycelium, and numerous chains of colorless 
gonidia are borne on short erect threads. The masses of gonidia 
give the leaf a powdery appearance. The mycelium lives on the 
outer surface of the leaf, but sends short haustoria into the epi- 
dermal cells. 

413. Fruit bodies of the willow mildew. — On this same myce- 
lium there appear later numerous black specks scattered over 
the affected places of the leaf. These are the fruit bodies (per- 
ithecia). If we scrape some of these from the leaf, and mount 
them in water for microscopic examination, we shall be able to 
see their structure. Examining these first with a low power of 
the microscope, each one is seen to be a rounded body, from 
which radiate numerous filaments, the appendages. Each one 
of these appendages is coiled at the end into the form of a little 
hook. Because of these hooked appendages this genus is called 
uncinula. This rounded body is the perithecium. 

i9S 



196 



MORPHOLOGY. 



414. Asci and ascospores — While we are looking at a few of 
these through the microscope with the low power, we should 




Fig. 225. 

Leaves of willow showing willow mildew. The black dots are the fruit bodies (perithecia) 

seated on the white mycelium. 

press on the cover glass with a needle until we see a few of the 
perithecia rupture. If this is done carefully we see several 
small ovate sacs issue, each containing a number of spores, as 
shown in fig. 227. Such a sac is an ascus, and the spores are 
ascospores. 



FUNGI: SAC FUNGI. 



197 



415. Number of spores in an ascus. — The ascus is the most important 
character showing the general relationship of the members of the sac fungi. 




Fig. 226. 
Willow mildew ; 
bit of myceliu m 
with erect conidio- 
phores, bearing 
chain of gonidia; 
gonidium at left 
germinating. 



Fig. 227. 

Fruit of willow mildew, showing hooked 

appendages. Genus uncinula. 

Figs. 227 228. — Perithecia (perithe- 
cium) of two powdery mildews, showing 
escape of asci containing the spores from 
the crushed fruit bodies. 



Fig. 228. 
Fruit body of an- 
other mildew with 
dichotomous ap- 
pendages. Genus 
microsphaera. 



While many of the powdery mildews have a variable number of spores in 




Fig. 229. 
Contact o f 
an th eridium 
and carpogo- 
nium (carpogo- 
nium the larger 
cell ) ; begin- 
ning of fertili- 
zation. 




Fig. 230. 

Disappear- 
ance of contact 
walls of anthe- 
r i d i u m and 
earpogonium, 
and fusion of 
the two nuclei. 




Fig. 231. 

Fertilized egc? surrounded 
by the enveloping threads 
whic 1 grow up around it. 
Figs. 229-231. — Fertilization in sphaerotheca; one of the powdery mildews. (After 

Harper.) 

an ascus, a large majority of the ascomyectes have just 8 spores in an 



198 



MORPHOLOGY. 



ascus, while some have 4. others 16, and some an indefinite number. 
The asci in a perithecium are more variable. In some ascomycetes there 
is no perithecium. 

416. The black fungi. — These are very common on dead logs, branches, 




Fig. 231a. 
Edible Morel. Morchella esculenta. The asci, forming hymenium, cover the 
pitted surface. 

leaves, etc., and may be collected in the woods at almost any season. The 
perithecia are often numerous, scattered or densely crowded as in Rosel- 



FUNGI: MUSHROOMS. 1 99 

linia. Sometimes they are united to form a crust which is partly formed 
from sterile elements as in Hypoxylon, or they form black clavate or 
branched bodies as in Xylaria. The black knot of the plum and cherry is 
also an example. 

The lichens are mostly ascomycetes like the black fungi or cup fungi, 
while a few are basidiomycetes. 

417. The morels (Morchella) . — There are several species of morels 
which are common in early spring on damp ground. Either one of the 
species is suitable for use if it is desired to include this in the study. Fig. 
231a illustrates the Morchella esculenta. The stem is cylindrical and 
stout. The fruiting portion forms the "head," and it is deeply pitted. 
The entire pitted surface is covered by the asci, which are cylindrical and 
eight spored. A thin section may be made of a portion for study, or a 
small piece may be crushed under the cover glass. 

418. The cup fungi. — These fungi are common on damp ground or on 
rotting logs in the summer. They may be preserved in 70 per cent alcohol 
for study. Many of them are shaped like broad open cups or saucers. 
The inner surface of the cup is the fruiting surface, and is covered with the 
cylindrical asci, which stand side by side. A bit of the cup may be sec- 
tioned or crushed under a cover glass for study. 

Mushrooms (Basidiomycetes). 

419. The large group of fungi to which the mushroom belongs is called 
the basidiomycetes because in all of them a structure resembling a club, 
or basidium, is present, and bears a limited number of spores, usually four, 
though in some genera the number is variable. Some place the rusts 
(Uredineae) in the same series (basidium series), because of the short pro- 
mycelium and four sporidia developed from each cell of the teleutospore. 

420. The gill-bearing fungi (Agaricaceae). — A good example 
for this study is the common mushroom (Agaricus campestris). 

This occurs from July to November in lawns and grassy fields. 
The plant is somewhat umbrella-shaped, as shown in fig. 232, 
■and possesses a cylindrical stem attached to the under side of the 
convex cap or pileus. On the under side of the pileus are thin 
radiating plates, shaped somewhat like a knife blade. These are 
the gills, or lamellae, and toward the stem they are rounded on 
the lower angle and are not attached to the stem. The longer 
ones extend from near the stem to the margin of the pileus, and 
the V-shaped spaces between them are occupied by successively 



200 



MORPHOLOGY. 




Fig. 232. 
Agaricus campestris. View of under side showing stem, annulus, gills, and margin of pileus. 




Fig. 233- 
Agaricus campestris. Longitudinal section through stem and pileus. a, pileus; 6, portion 
pf veil on margin of pileus ; c, gill ; /, fragment of annulus ; e, stipe. 



FUNGI: MUSHROOMS. 



20 1 



shorter ones. Around the stem a little below the gills is a collar, 
termed the ring or annulus. 

421. Fruiting surface of the mushroom. — The surface of 
these gills is the fruiting surface of the mushroom, and bears the 
gonidia of the mushroom, which are dark purplish brown when 
mature, and thus the gills when old are dark in color. If we make 
a thin section across a few of the gills, we see that each side of 
the gill is covered with closely crowded club-shaped bodies, each 
one of which is a basidium. In fig. 234 a few of these are en- 
larged, so that the 
structure of the gill 
can be seen. Each 
basidium of the com- 
mon mushroom has 




Fig. 234. 
Portion of section of lamella of Agaricus campestris. 
tr, trama ; sh, subhymenium ; />, basidium; st, sttrigma 
(//. sterigmata) ; g; basidiospore. 



Fig. 235. 
Portion of liymenium of Co- 
prinus micaceus, showing large 
cystidium in the liymenium. 



two spinous processes at the free end. Each one is a slerig'?na 
(plural slerig'mala), and bears a gonidium. In a majority of the 
members of the mushroom family each basidium bears four 
spores. When mature these spores easily fall away, and a mass 
of them gives a purplish-black color to objects on which they fall, 
so that a print of the under surface of the cap showing the 
arrangement of the gills can be obtained by cutting off the stem, 
and placing the pileus on white paper for a time. 

422. How the mushroom is formed. — The mycelium of the 



202 



MORPHOLOGY. 




FUNGI: MUSHROOMS 



203 



mushroom lives in the ground, and grows here for several months 
or even years, and at the proper seasons develops the mature 
mushroom plant. The mycelium lives on decaying organic mat- 
ter, and a large number of the threads grow closely together form- 
ing strands, or cords, of mycelium, which are quite prominent 
if they are uncovered by removing the soil, as shown in fig. 236. 
423. From these strands the buttons arise by numerous threads 
growing side by side in a vertical direction, each thread growing 
independently at the end, but all lying very closely side by 




Fig. 237. 
Agaricus campestris ; sections of "buttons" of different sizes, showing formation of gills 
and veil covering them. 

side. When the buttons are quite small the gills begin to form 
on the under margin of the knob. They are formed by certain 
of the threads growing downward in radiating ridges, just as many 
of these ridges being started as there are to be gills formed. At 
the same time, threads of the stem grow upward to meet those at 
the margin of the button in such a manner that they cover up 
the forming gills, and thus enclose the gills in a minute cavity. 
Sections of buttons at different ages will show this, as is seen 
in fig. 237. This curtain of mycelium which is thus stretched 
across the gill cavity is the veil. As the cap expands more 
and more this is stretched into a thin and delicate texture as 



204 MORPHOLOGY. 

shown in fig. 238. Finally, as shown in fig. 239, this veil is 
ruptured by the expansion of the pileus, and it either clings 




Fig. 238. 
Agaricus campestris ; nearly mature plants, showing veil still stretched across the gill 
cavity. 




Fig. 239- 
Agaricus campestris ; under view of two plants just after rupture of veil, fragments of the 
latter clinging both to margin of pileus and to stem. 



FUNGI: MUSHROOMS. 



205 




Fig. 240. 

Agaricus campestris ; plant in natural position just after rupture of veil, showing tendency 
to double annulus on the stem. Portions of the veil also dripping from margin of pileus. 




Fig. 241. 
Agaricus campestris ; spore print. 



2o6 



MORPHOLOGY. 



B 

r+ C 



3 <W 

£ 5" *■ 

"O re w 
a 3 ' 



^ 3 

5' en 




FUNGI: MUSHROOMS. 20"J 

to the stem as a collar, or a portion of it remains clinging to 
the margin of the cap. When the buttons are very young 
the gills are white, but they soon become pink in color, and 




Fig. 243. 
Amanita phalloides ; white form, showing pileus, stipe, annulus, and volva. 

very soon after the veil breaks the spores mature, and then 
the gills are dark brown. 

424. Beware of the poisonous mushroom. — The number of 
species of mushrooms, or toadstools as they are often called, is 
very great. Besides the common mushroom (Agaricus campes- 



208 



MORPHOLOGY. 



tris) there are a large number of other edible species. But 
one should be very familiar with any species which is gathered 
for food, unless collected by one who certainly knows what the 
plant is, since carelessness in this respect sometimes results fatally 
from eating poisonous ones. 

425. A plant very similar in structure to the Agaricus campes- 
tris is the Lepiota naucina, but the spores are white, and thus the 
gills are white, except that in age they become a dirty pink. 
This plant occurs in grassy fields and lawns often along with the 




Fig. 244. 
Amanita phalloides ; plant turned to one side, after having been placed in a horizontal 
position, by the directive force of gravity. 



common mushroom. Great care should be exercised in collect- 
ing and noting the characters of these plants, for a very deadly 
poisonous species, the deadly amanita (Amanita phalloides) is 
perfectly white, has white spores, a ring, and grows usually in 
wooded places, but also sometimes occurs in the margins of lawns. 
In this plant the base of the stem is seated in a cup -shaped struc- 
ture, the volva, shown in fig. 243. One should dig up the stem 
carefully so as not to tear off this volva if it is present, for with 
the absence of this structure the plant might easily be mistaken 
for the lepiota, and serious consequences would result. 



FUNGI: MUS&fiOOMS. 



209 



426. Tube-bearing fungi (Polyporaceae). — In the tube-bearing fungi, the 
fruiting surface, instead of lying over the surface of gills, lines the surface 
of tubes or pores on the under side of the cap. The fruit-bearing portion 
therefore is "honey-combed." The sulphur polyporus (Polyporus sulphu- 
reus) illustrates one form. The tube-bearing fungi are sometimes called 
"bracket" fungi, or "shelf" fungi, because the pileus is attached to the 




Edible Boletus, 
side of cap. 



Fig. 245- 
Boletus edulis. Fruiting surface honey-combed on under 



tree or stump like a shelf or bracket. One very common form in the woods 
is the plant so much sought by "artists," and often called Polyporus ap- 
planatus. It is hard and woody, reddish brown, brown or grayish on the 
upper side, according to age, and is marked by prominent and large concentric 
ridges. (This form is probably P. leucophaeus.) The under side is white 
and honey-combed by numerous very minute pores. This plant is peren- 
nial, that is, it lives from year to year. Each year a new layer is added to 
the under side, and several new rings usually to the margin. If a plant 
two or three years old is cut in two, there will be seen several distinct tube 
layers or strata, each one representing a year's growth. 

In some of these bracket fungi, each ring on the upper surface marks a 



2 1 MORPHOLOG Y. 

year's growth as in the pine polyporus (P. pinicola). In the birch poly- 

porus (P. fomentarius) the tubes are quite large. It also occurs on other 

trees. The beech polyporus (P. igniarius, also on other trees) often be- 





. ■' '•-^^r^^ji^^^ 








£n| 


B/j^^ 






- 

1 i# 




^ oi 


a& .' 




- ^> -"^j 




kL~" ** ' ^ - • J& 





Fig. 246. 
Coral fungus. Hydnum coralloides, spines hanging down from branches. 

comes very old. I have seen one specimen over eighty years old. Not all 
the tube-bearing fungi are bracket form. Some have a stem and cap 
(see fig. 245). Some are spread on the surface of logs. 

427. Hedgehog fungi (Hydnacese). — These plants are bracket in form or 
have a stem and cap, or are spread on the surface of wood; but the finest 
specimens resemble coral masses of fungus tissue (example, Hydnum, fig. 
246). In most of them there are slender processes resembling teeth, spines 
or awls, which depend from the under surface (fig. 247). The fruiting 
surface covers these spines. ^ 

428. Coral fungi or fairy clubs (Clavariaceae). — These plants stand 
upright from the wood, leaves, or soil, on which they grow (example, 
Clavaria). The "coral" ones are branched, while the "fairy clubs" are 
simple. The fruiting surface covers the entire exposed surface of the plants 
(hg. 248). 



FUNGI: MUSHROOMS. 



211 




Fig. 247. 
Hydnum rcpandum, spines hanging down from under side of cap. 



212 MORPHOLOGY. 




Fig. 248. 
Clavaria botrytes. 



CHAPTER XXII. 



CLASSIFICATION OF THE FUNGI. 



429. Classification of the fungi. — Those who believe that the fungi repre- 
sent a natural group of plants arrange them in three large series related to 
each other somewhat as follows •. 

The Basidium Type or Series. 
The number of gonidia on a ba- 
sidium is limited and definite, 
and the basidium is a characteris- 
tic structure; examples: uredineae 
(rusts), mushrooms, etc. 

The Ascus Type or Series. The 
number of spores in an ascus is 
limited and definite, and the ascus is 
a characteristic structure; examples: 
leaf curl of peach (exoascus), pow- 
dery mildews, black knot of plum, 
black rot of grapes, etc. 

430. Others believe that the fungi do not represent a natural group, but 
that they have developed off from different groups of the algae by becoming 
parasitic. As parasites they no longer needed chlorophyll, and conse- 
quently lost it. 

According to this view the lower fungi have developed off from the lower 
algae (saprolegnias, mucors, peronosporas, etc., being developed off from 
siphonaceous algae like vaucheria), and the higher fungi being developed 
off from the higher algae (the ascomycetes perhaps from the Rhodophyceae) . 

431. A very general outline of classification,* according to the former of 



The Gonidium Type or Series. 
The number of gonidia in the spo- 
rangium is indefinite and variable. 
It may be very large or very small, 
or even only one in a sporangium. 
To this series belong the lower 
fungi; examples: mucor, saprolegnia, 
peronospora, etc. 



* Class Myxomycetes, or Myoetozoa. — To this class belong the "slime 
molds," low organisms consisting of masses of naked protoplasm which 
flows among decaying leaves and in decaying wood, coming to the surface 
to fruit. The fruit in many cases resembles miniature puff-balls, and these 
plants were formerly classed with the puff-balls. The spores germinate by 

213 



214 



MORPHOLOGY. 



these views, might be presented here to show the general relationships of 
the fungi studied, with the addition of a few more in orders not represented 
above. It should be borne in mind that the author in presenting this view 
of classification does not necessarily commit himself to it. It is based 
on that presented in Engler & Prantl's Pflanzenfamilien. There are three 
classes. 

I. Class Phycomycetes (Alga-like Fungi). 

1. SUBCLASS OOMYCETES. 
432. These are the egg-spore fungi. They include the water mold 
(Saprolegnia), the downy mildew of the grape (Plasmopara), the potato 




Fig. 249. 
Chytrids. A, Harpochytrium hedenii, parasitic on spirogyra threads; a, sickle- 
form plant; b, the sporangium part with escaping zoospores; c, old plant pro- 
liferating by forming new sporangium in the old empty one; d, zoospore; 0, two 
young plants just beginning to grow. B, Rhizophidium globosum parasitic on 
spirogyra. Globose sporangium with delicate threads inside of the host, zoospores 
escaping from one. C, Olpidium pendulum, parasitic in spirogyra cell. Ellip- 
tical sporangium with slender exit tube through which zoospores are escaping. 
D, Lagenidium rabenhorstii parasitic in spirogyra cell. Two slender sporangia 
with exit tubes through which protoplasm escapes forming a rounded mass at the 
end of tube, this protoplasm forming biciliate zoospores. 



forming swarm spores which unite to form a small plasmodium, which in 
turn grows to form a large plasmodium or protoplasmic mass. It is doubt- 
ful if they are any more plant than animal organisms. Examples: Trichia, 
Arcyria, Stemonitis, Physarum, Ceratiomyxa, etc., on rotten wood; Plas- 
modiophora brassicae is a parasite causing club foot of cabbage, radishes, 
etc. It lives within the roots, causing large knots and swellings on the same. 



FUNGI CONTINUED; CLASSIFICATION. 



215 



blight (Phytophthora), the white rust of cruciferous plants (Cystopus = 
Albugo), the damping-off fungus (Pythium), and many parasites of the 
algae known as chytrids, as Olpidium, Rhizophidium, Lagenidium, Chytri- 
dium, etc. 

The two following orders are sometimes placed in a separate subclass, 
Archimycetes. 

433. Order Chytridiales (Chytridineae). — These include the lowest fungi. 
Many of them are parasitic on algae and lack mycelium, the swarm spore 
either with or without minute rhizoids, developing into a globose sporan- 
gium (Rhizophidium, Chytridium, Olpidium, etc., fig. 249), or the swarm 
spore attached to the wall of the host develops into a long sword-shaped 
body with a sterile base, which proliferates ..•••■•>;. 

and forms a new sporangium in the old one 
(Harpochytrium), or with slight develop- 
ment of mycelium in aquatic plants (Cla- 
dochytrium). Some are parasitic in leaves 
and stems of land plants. Synchytrium 
decipiens is very common on the trailing 
legume, Amphicarpasa monoica. 

434. Order Ancylistales (Ancylistinese). 
— The members of this order have a slight 
development of mycelium and many are 
parasitic in algae (Lagenidium, fig. 249). 

435. Order Saprolegniales (Saproleg- 
niinese). — These include the water molds 
(Saprolegnia). See Chapter XIX. 

436. Order Monoblepharidales (Mono- 
blepharidineee). — These are peculiar water 
molds, related to the Saprolegniales, but 
motile sperm cells are formed (Monoble- 
pharis, etc., fig. 250). 

437. Order Peronosporales (Peronospori- 
nese). — These include the downy mildews 
(Peronospora, Plasmopara, Phytopthora, 
etc.), and the white rust of crucifers and 
other plants (Cystopus= Albugo), Chapter XIX. 








Fig. 250. 
Monoblepharis insignis Thax- 
ter. End of hypha bearing oogo- 
nium (oog) and antheridium (ant) 
Sperms escaping from antheridium 
and creeping up on the oogonium. 
(After Thaxter.) 



2. SUBCLASS ZYGOMYCETES. 

438. These are the conjugating fungi. 

439. Order Mucorales (Mucorineae).— This includes the black mold and 
its many relatives (Mucor, Rhizopus, etc.). Chapter XIX. 

440. Order Entomophthorales (Entomophthorineae). — This order in- 
cludes the "fly fungus" (Empusa) and its many relatives parasitic on insects. 



2l6 



MORPHOLOGY. 



In the autumn and winter dead flies are often found stuck to window-panes, 
with a white ring of the conidia around each fly. 

II. Class Ascomycetes. (The ascus series.) 

1. SUBCLASS HEMIASCOMYCETES. 
441. Order Hemiascales (Hemiascineae). — Fungi with a well developed, 

septate mycelium, but 
with a sporangium-like 
ascus, i.e., a large and 
indefinite number of 
spores in the ascus. Ex- 
amples : Protomyces 
macrosporus in stems of 
Umbelliferae, or P. poly- 
sporus in Ambrosia tri- 
fida. These two are by 
some placed in the Usti- 
lagineae. Dipodascus 
albidus grows in the 
exuding sap of Bromeli- 
acese in Brazil and the 
sap of the beech in 
Sweden. The ascus is 
developed as the result 
of the fertilization of an 
ascogonium with an an- 

scoa theridium (see fig - 25l) - 

^ 2. SUBCLASS 

PROTOASCOMYCETES. 
442. The a sci are well 
defined and usually with 
a limited and definite 
number of spores (usu- 
ally 8, sometimes i, 2, 
Mycelium often well developed and septate. Asci scat- 




Fig. 251. 
Dipodascus albidus. A, thread with sexual organs, 
ascogonium and antheridium ; B , fertilized ascogonium 
developing ascus; C, ascus with spores; D, conidia. 
(After Lagerheim.) 



4, 16, or more) 

tered on the mycelium, not associated in definite fields or groups. 

443. Order Protoascales (Protoascineae) . — The asci are separate cells, 
or are scattered irregularly in loose wefts of mycelium. No fruit body. 
(The yeast, Saccharomyces, see paragraph 237; and certain mold-like 
fungi, some of which are parasitic on mushrooms, as Endomyces, are 
examples.) 



FUNGI CONTINUED: CLASSIFICATION. 21? 

3. SUBCLASS EUASCOMYCETES. 

Asci associated in surfaces forming a hymenium, or in groups or inter- 
mingled in the elements of a fruit body. Fruit body usually present. 

The following four or five orders comprise the Discomycetes, according 
to the usual classification. 

444. Order Protodiscales (Protodiscineae). — The asci are exposed and 
form large and indefinite groups, but there is no definite fruit body. Ex- 
amples: leaf curl of peach, plum pocket, etc. (Exoascus). 

445. Order Helvellales (Helvellineae). — The asci form large fields over 
the upper portion of the fruit body. This order includes the morels (fig. 
231a), helvellas, earth tongues (Geoglossum), etc. 

446. Order Pezizales (Pezizineae). — The asci form a definite field or 
fruiting surface surrounded on the sides and below by a wall of fungus tis- 
sue, forming a fruit body in the shape of a cup. These are known as the 
cup fungi (Peziza, Lachnea, etc.). 

447. Ordsr Phacidiales (Phacidiineae). — Fungi mostly saprophytic, and 
fruit body similar to the cup fungi. Examples: Propolis in rotting wood, 
Rhytisma forming black crusts on leaves (maple for example), Urnula 
craterium, a large black beaker-shaped fungus on the ground. 

448. Order Hysteriales (Hysteriineae). — Fungi with a more or less elon- 
gated fruit body with an enclosing wall opening by a long slit. In some 
forms the fruit body has the appearance of a two-lipped body; in others 
it is shaped like a clam shell, the asci being inside. Example, Hystero- 
graphium common on dry, dead, decorticated sticks. 

449. Order Tuberales (Tuberineae). — The more or less rounded fruit 
bodies are usually subterranean. The most important fungi in this order 
are the truffles (Tuber). The mycelium of many species assists in the 
formation of mycorhiza on the roots of oaks, etc., and several species are 
partly cultivated, or protected, and collected for food. This is especially 
the case with Tuber brumale and its forms; more than a million francs 
worth of truffles are sold in France and Italy yearly. Dogs and pigs are 
employed in the collection of truffles from the ground. 

450. Order Plectascales (Plectascineae). — The fruit body of these plants 
is more or less globose, and contains the asci distributed irregularly through 
the mycelium of the interior. Some are subterranean (Elaphomyces), 
while others grow in decaying plants, or certain food substances (Euro- 
tium, Sterigmatocystis, Penicilhum). Penicilhum in its conidial stage 
forms blue mold on fruit, bread, etc. 

The following four orders comprise the Pyrenomycetes, according to the 
usual classification. 

451. Order Perisporiales. — The powdery mildews are good examples of 
this order (Uncinula, Microsphaera, etc., Chapter XXI). 



2 1 8 MORPHOL OGY. 

452. Order Hypocreales.* — The fruit bodies are colorless, or bright 
colored and entirely enclose the asci, sometimes opening by an apical pore. 
Nectria cinnabarina has clusters of minute orange oval fruit bodies, and is 
common on dead twigs. Cordyceps with a number of species is parasitic 
on insects, and on certain subterranean Ascomycetes, especially Elapho- 
myces (of the order Plectascales= PlectascinecE). 

453. Order Dothidiales.*— Fungi with black stroma formed of mycelium 
in which are cavities containing the asci. The cavities are usually shaped 
like a perithecium, but there is no wall distinct from the tissue of the stroma 
(Dothidea, Phyllachora, on grasses). 

454. Order Sphaeriales.* — These contain the so-called black fungi, with 
separate or clustered, oval, fruit bodies, black in color. The black wall 
encloses the asci, and usually opens by an apical pore. Examples are 
found in the black knot of plum and cherry, black rot of grapes, and in 
Rosellinia, Hypoxylon, Xylaria, etc., on dead wood. 

455. Order Laboulbeniales (Laboulbineae). — These are peculiar fungi 
attached to the legs and bodies of insects by a short stalk, and provided 
with a sac-like fruit body which contains the asci. Example, Laboulbenia. 

III. Class Basidiomycetes. (The basidium series.) 

1. SUBCLASS HEMIBASIDIOMYCETES. 

456. Order Ustilaginales (TJstilagineae). — This order includes the well- 
known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.). 

2. SUBCLASS JECIDIOMYCETES. 

457. Order Uredinales f (Uredineae). — This order includes the parasitic 
fungi known as rusts. Examples: wheat rust (Chapter XX), the cedar 
apple, etc. 

The true Basidiomycetes include the following orders: 

3. SUBCLASS PROTOBASIDIOMYCETES. 

458. Order Auriculariales.f — This order includes trembling fungi in 
which the basidium is long and divided transversely into usually four cells 
(example, Auricularia), and similar forms. Pilacre petersii on dead wood 
represents an angiocarpous form. 

459. Order Tremellales (Tremellineae), trembling or gelatinous fungi 
with the globose basidium divided longitudinally into four cells (Tremella) . 



* As suborder in Engler and Prantl. 

f The Uredinales and Auriculariales in Engler and Prantl are placed iii 
order, Auriculariineae. 



FUNGI CONTINUED: CLASSIFICATION. 2ig 

4. SUBCLASS EUBASIDIOMYCETES. 

460. Order Dacryomycetales (Dacryomycetineae). — This order includes 
certain fungi of a gelatinous or waxy consistency, usually of bright colors. 
They resemble the Tremellales, but the basidia are slender and fork into 
two long sterigmata. (Example, Dacryomyces.) Gyrocephalus rufus is 
quite a large plant, 10-15 cm - high, growing on the ground in woods. 

461. Order Exobasidiales (Exobasidiineae). — The fungus causing azalea 
apples is an example (Exobasidium). 

462. Order Hymeniales (Hymenomycetineae). — In this order the basidia 
are usually club-shaped and undivided, and bear usually four spores on 
the end (sometimes two or six). There are several families. 

463. Family Thelephoraceae. — The fruit bodies are more or less mem- 
branous and spread over wood or the ground, or somewhat leaflike, grow- 
ing on wood or the ground. The fruiting surface is nearly or quite even, 
and occupies the under side of the leaflike bodies (Stereum, Thelephora) 
or the outside of the forms spread out on wood (Corticium, Coniophora). 

464. Family Clavariaceae. — This order includes the fairy clubs, and some 
of the coral fungi. The larger number of species are in one genus (Clava- 
ria, fig. 248). 

465. Family Hydnaceae. — The fungi of this order are known as "hedge- 
hog" fungi, because of the numerous awl-like teeth or spines over which 
the fruiting surface is spread, as in Hydnum (figs. 246, 247). 

466. Family Polyporaceae. — The tube-bearing fungi (Polyporus, Bole- 
tus, etc., fig. 245). 

467. Family Agaricaceae. — The gill-bearing fungi (Agaricus, Amanita, 
etc., see Chapter XXI). 

The above five orders, according to the earlier classification (still used at 
the present time by some), made up the order Hymenomycetes, while the 
following five orders made up the Gasteromycetes. The Hymenomycetes, 
according to this system, included those plants in which the fruiting portion 
(hymenium) is either exposed from the first, or if covered by a veil or volva 
(as in Agaricus, Amanita, etc.) this ruptures and exposes the fruiting sur- 
face before, or at the time of, the ripening of the spores, while the Gaster- 
omycetes included those in which the fruit body is closed until after the 
maturity of the spores. 

468. Order Phallales (Phallineae). — The "stink-horn" fungi, or "buz- 
zard's nose." Usually foul-smelling fungi, the fruiting portion borne aloft 
on a stout stalk, and dissolving (Dictyophora, Ithyphallus, etc.). 

469. Order Hymenogastrales (Hymenogastrineae). — The basidia form a 
distinct hymenium which does not break down at maturity. Some of the 
plants resemble Boletus or Agaricus in the way the fruit bodies open (Seco- 
tium, etc.), while others open irregularly on the surface (Rhizopogon) or 



220 ' MORPHOLOGY. 

y 
like an earth star (Sclerogaster), or portions of the surface become gelatin* 
ized (Phallogaster). The last-named one grows on very rotten wood, while 
most of the others grow on the ground. 

470. Order Lycoperdales (Lycoperdineae). — These include the " puff- 
balls," or "devil's snuff-box" (Lycoperdon), and the earth stars (Geaster). 
The basidia form a distinct hymenium, but at maturity the entire inner por- 
tion of the plant (except certain peculiar threads, the capillitium) disinte- 
grates and with the spores forms a powdery mass. 

471. Order Nidulariales (Nidulariinese). — These are known as bird-nest 
fungi. The fruit body when mature is cup-shaped, or goblet-shaped, and 
contains minute flattened circular bodies (peridiola) containing the spores. 
The intermediate portions of the fruit body disintegrate and set the peri- 
diola free, which then lie in the cup-shaped base like eggs in a nest. 

472. Order Plectobasidiales (Plectobasidiinese). — The basidia do not 
form a definite hymenium, but are interwoven with the threads inside, or 
are collected into knot -like groups. (Examples: Calostoma, Tulostoma, 
Astraeus, Sphserobolus, etc.) 

472a. Lichens. — The plant body of the lichens (see paragraphs 200, 
201) consists of two component parts, the one a fungus, the other an alga. 
The fructification is that of the fungus. The fruit body shows the lichens 
to be related some to the Ascomycetes, others to the Hymenomycetes, and 
Gasteromycetes. They are usually classified as a distinct class or order 
from the fungi, but a natural arrangement would distribute them in sev- 
eral of the orders above. Their special relationship with these orders has 
not been satisfactorily worked out. For the present they are arranged as 
follows: 
Ascolichenes. 

Pyrenocarpous lichens (those with a fruit body like the Pyrenomycetes). 

Gymnocarpous lichens (those with a fruit body like the Discomycetes). 
Hymenolichenes (those with a fruit body like the Hymenomycetes). 
Gasterolichenes (those with a fruit body like the Gasteromycetes). 

From a vegetative standpoint there are two types according to the dis- 
tribution of the elements. 

1 st. Where the fungal and algal elements are evenly distributed in the 
plant body the lichen is said to be homoiomerous. There are two types of 
these: 

a. Filamentous lichens, example, Ephebe pubescens. 

b. Gelatinous lichens, example, Collema (with the alga nostoc), Physma 
(with the Chroococcacese). 

2d. Where the elements are stratified, as in Parmelia, etc., the lichen is 
said to be heteromerous. In these there are three types: 

a. Crustaceous lichens, the plant body is in the form of a thin incrusta- 
tion on rocks, etc. 



FUNGI CONTINUED: CLASSIFICATION. 



221 



b. Foliaceous lichens, the plant body is leaflike and lobed and more or less 
loosely attached by rhizoids: Parmelia, Peltigera, etc. 




Fig. 251a. 
Rock lichen (Parmelia contigua). 



c. Fruticose lichens, the plant body is filamentous or band-like and 
branched, as in Usnea, Cladonia, etc. 



CHAPTER XXIII. 

LIVERWORTS (HEPATICyE). 

473. We come now to the study of representatives of another 
group of plants, a few of which we examined in studying the organs 
of assimilation and nutrition. I refer to what are called the liver- 
worts. Two of these liverworts belonging to the genus riccia 
are illustrated in figs. 30, 252. 

Riccia. 

474. Form of the floating riccia (R. fluitans). — The gen- 
eral form of floating riccia is that of a narrow, irregular, flattened, 
ribbon-like object, which forks repeatedly, in a dichotomous 
manner, so that there are several lobes to a single plant. It 
receives its name from the fact that at certain seasons of the year 
it may be found floating on the water of pools or lakes. When 
the water lowers it comes to rest on the damp soil, and rhizoids 
are developed from the under side. Now the sexual organs, and 
later the fruit capsule, are developed. 

475. Form of the circular riccia (R. crystallina). — The 
circular riccia is shown in fig. 252. The form of this one is quite 
different from the floating one, but the manner of growth is much 
the same. The branching is more compact and even, so that a cir- 
cular plant is the result. This riccia inhabits muddy banks, 
lying flat on the wet surface, and deriving its soluble food by 
means of the little rootlets (rhizoids) which grow out from the 
under surface. 

Here and there on the margin are narrow slits, which extend 



LIVERWORTS: RICCIA. 



223 




Fig. 252. 
Thallus of Riccia crystallina. 



nearly to the central point. They are not real slits, however, for 
they were formed there as the plant grew. Each one of these 
V-shaped portions of the thal- 
lus is a lobe, and they were 
formed in the young condition 
of the plant by a branching 
in a forked manner. Since 
growth took place in all direc- 
tions radially the plant be- 
came circular in form. These 
large lobes we can see are 
forked once or twice again, 
as shown by the seeming 
shorter slits in the margin. 

476. Sexual organs. — In 
order to study the sexual organs we must make thin sections 
through one of these lobes lengthwise and perpendicular to the 
thallus surface. These sections are mounted for examination 
with the microscope. 

477. Archegonia. — We are apt to find the organs in various stages of de- 
velopment, but we will select one of the flask-shaped structures shown in fig. 
253 for study. This flask-shaped body we see is entirely sunk in the tissue 
of the thallus. This structure is the female organ, and is what we term in 
these plants the archegonium. It is more complicated in structure than the 
oogonium. The lower portion is enlarged and bellied out, and is the venter 
of the archegonium, while the narrow portion is the neck. We here see it in 
section. The wall is one cell layer in thickness. In the neck is a canal, 
and in the base of the venter we see a large rounded cell with a distinct 
and large nucleus. This cell is the egg cell. 

478. Antheridia. — The antheridia are also borne in cavities sunk in the 
tissue of the thallus. There is here no illustration of the antheridium of this 
riccia, but fig. 259 represents an antheridium of another liverwort, and there 
is not a great difference between the two kinds. Each one of those little rect- 
angular sperm mother cells in the antheridium changes into a swiftly moving 
body like a little club with two long lashes attached to the smaller end By 
the violent lashing of these organs the spermatozoid is moved through the water, 
or moisture which is on the surface of the thallus. It moves through the canal 
of the archegonium neck and into the egg, where it fuses with the nucleus of 
the egg, and thus fertilization is effected. 



224 



MORPHOLOG V. 



479. Embryo. — In the plants which we have selected thus far for study, 
the egg, immediately after fecundation, we recollect, passed into a resting 
state, and was enclosed by a thick protecting wall. But in riccia, and in the 
other plants of the group which we are now studying, this is not the case. 





Frj. 253. 
Archegonium of riccia, showing neck, 
venter, and the egg; archegonium is partly 
surrounded by the tissue of the thallus. 
(Riccia crystallina.) 



Fig. 254. 
Young embryo (sporogoni- 
um) of riccia, within the venter 
of the archegonium ; the latter 
has now two layers of cells. 
(Riccia crystallina.; 



The egg, on the other hand, after acquiring a thin wall, swells up and fills 
the cavity of the venter. Then it divides by a cross wall into two cells. 
These two grow, and divide again, and so on until there is formed a quite 
large mass of cells rounded in form and still contained in the venter of the 
archegonium, which itself increases in size by the growth of the cells of the 
wall. 

480. Sporogonium of riccia. — The fruit of riccia, which is 
developed from the fertilized egg in the archegonium, forms a 
rounded capsule still enclosed in the venter of the archegonium, 
which grows also to provide space for it. Therefore a section 
through the plant at this time, as described for the study 
of the archegonium, should show this capsule. The capsule 
then is a rounded mass of cells developed from the egg. A sin- 
gle outer layer of cells forms the wall, and therefore is sterile. 



LIVERWORTS: RICCIA. 



225 



All the inner cells, which are richer in protoplasm, divide into 
four cells each. Each of these cells becomes a spore with a thick 
wall, and is shaped like a triangular pyramid whose sides are of 
the same extent as the base (tetrahedral). These cells formed in 






Nearly mature sporogonium of Riccia crystallina ; 
mature spore at the right. 



Fig. 256. 
Riccia glauca ; archegonium 
containing nearly mature spo- 
rogonium. sg, spore-producing 
cells surrounded by single layer 
of sterile cells, the wall of the 
sporogonium. 



fours are the spores. At this time the wall of the spore-case dis- 
solves, the spores separate from each other and fill the now en- 
larged venter of the archegonium. When the thallus dies they 
are liberated, or escape between the loosely arranged cells of 
the upper surface. 

481. A new phase in plant life. — Thus we have here in the 
sporogonium of riccia a very interesting phase of plant life, in 
which the egg, after fertilization, instead of developing directly 
into the same phase of the plant on which it was formed, 
grows into a quite new phase, the sole function of which is the 
development of spores. Since the form of the plant on which the 
sexual organs are developed is called the gametophyie, this new 
phase in which the spores are developed is termed the sporo- 
phyte. 

Now the spores, when they germinate, develop the gameto- 
phyte, or thallus, again. So we have this very interesting condi- 



226 MORPHOLOG Y. 

tion of things, the thallus (gametophyte) bears the sexual organs 
and the unfertilized egg. The fertilized egg, starting as it does 
from a single-celled stage, develops the sporogonium (sporo- 
phyte). Here the single-cell stage is again reached in the spore, 
which now develops the thallus. 

482. Riccia compared with coleochaete, cedogonium, etc. — We have said 
that in the sporogonium of riccia we have formed a new phase in plant life. 
If we recur to our study of coleochaete we may see that there is here possibly 
a state of things which presages, as we say, this new phase which is so well 
formed in riccia. We recollect that after the fertilized egg passed the period 
of rest it formed a small rounded mass of cells, each of which now forms a 
zoospore. The zoospore in turn develops the normal thallus (gametophyte) 
of the coleochaete again. In coleochsete then we have two phases of the 
plant, each having its origin in a one-celled stage. Then if we go back 
to cedogonium, we remember that the fertilized egg, before it developed 
into the cedogonium plant again (which is the gametophyte), at first divides 
into /our cells which become zoospores. These then develop the cedogonium 
plant. 

Note. Too much importance should not be attached to this seeming ho- 
mology of the sporophyte of cedogonium, coleochsete, and riccia, for the nu- 
clear phenomena in the formation of the zoospores of cedogonium and coleo- 
chaete are not known. They form, however, a very suggestive series. 



Marchantia. 

483. The marchantia (M. polymorpha) has been chosen for 
study because it is such a common and easily obtained plant, and 
also for the reason that with comparative ease all stages of 
development can be obtained. It illustrates also very well cer- 
tain features of the structure of the liverworts. 

The plants are of two kinds, male and female. The two dif- 
ferent organs, then, are developed on different plants. In 
appearance, however, before the beginning of the structures 
which bear the sexual organs they are practically the same. The 
thallus is flattened like nearly all of the thalloid forms, and 
branches in a forked manner. The color is dark green, and 
through the middle line of the thallus the texture is different 
from that of the margins, so that it possesses what we term a 



LIVER WOR TS : MA R CHA N TIA . 



227 



midrib, as shown in figs. 257, 261. The growing point of the 
thallus is situated in the little depression at the free end. If we 
examine the upper surface with a hand 
lens we see diamond-shaped areas, and 
at the center of each of these areas are 
the openings known as the stomates. 

484. Antheridial plants. — One of 
the male plants is figured at 257. It 
bears curious structures, 
each held aloft by a short 
stalk. These are the an- 
theridial recep- 
tacles (or male 
gametophores). 
Each one is cir- 
cular, thick, and 
shaped some- Fig. 257. 

what like a bi" Male plant of marchantia bearing antheridiophores. 

convex lens. The upper surface is marked by radiating fur- 
rows, and the margin is crenate. Then we note, on careful 
examination of the upper surface, that there are numerous minute 
openings. If we make a thin section of this structure perpen- 





Fig. 258. 
Section of antheridial receptacle from male plant of Marchantia polymorpha, showing 
cavities where the antheridia are borne. 

dicular to its surface we shall be able to unravel the mystery of 
its interior. Here we see, as shown in fig. 258, that each one 
of these little openings on the surface is an entrance to quite 



228 



MORPHOLOGY. 



a large cavity. Within each cavity there is an oval or ellip- 
tical body, supported from the base of the cavity on a short 
stalk. This is an antheridium, and one of them is shown still 
more enlarged in fig. 259. This shows the structure of the 
antheridium, and that there are within several angular areas, 
which are divided by numerous straight cross-lines into countless 
tiny cuboidal cells, the sperm mother cells. Each of these, as 
stated in the former chapter, changes into a swiftly moving body 
resembling a serpent with two long lashes attached to its tail. 

485. The way in which one of these sperm mother cells changes into this 
spermatozoid is very curious. We first note that a coiled spiral body is appear- 




Fig-. 250. 
Section of antheridium of mar- 
chantia, showing the groups of 
sperm mother cells. 



Fig. 260. 
Spermatozoids of marchantia, 
uncoiling and one extended, show- 
ing the two cilia. 



ing within the thin wall of the cell, one end of the coil larger than the other. 
The other end terminates in a slender hair-like outgrowth with a delicate vesi- 
cle attached to its free end. This vesicle becomes more and more extended 
until it finally breaks and forms two long lashes which are clubbed at their 
free ends as shown in fig. 260. 

486. Archegonial plants. — In fig. 261 we see one of the 
female plants of marchantia. Upon this there are also very 
curious structures, which remind one of miniature umbrellas. 
The general plan of the archegonial receptacle (or female 



LI VER WOR TS : MA R CHA N TIA . 



229 



gametophore), for this is what these structures are, is similar to 
that of the antheridial receptacle, but the rays are more pro- 
nounced, and the details of structure are quite different, as we 
shall see. Underneath the arms there hang down delicate 
fringed curtains. If we make sections of this in the same direc- 




Fig. 261. 
Marchantia polymorpha, female plants bearing archegoniophores. 

tion as we did of the antheridial receptacle, we shall be able to 
find what is secreted behind these curtains. Such a section is 
figured at 266. Here we find the archegonia, but instead of 
being sunk in cavities their bases are attached to the under 



230 



MORPHOLOG Y. 



surface, while the delicate, pendulous fringes afford them pro- 
tection from drying. An archegonium we see is not essentially 
different in marchantia from what it is in riccia, and it will be 
interesting to learn whether the sporogonium is essentially dif- 
ferent from what we find in riccia. 

487. Homology of the gametophore of marchantia. — To see the relation 

of the gametophore to the thallus of 
marchantia take portions of the 



thallus bearing the female recepta- 
cle. On the under side note that 
the prominent midrib continues be- 
yond the thin lateral expansions and 
arches upward in the sinus or notch 
at the end, or at the side where the 
branch of the thallus has continued 
to grow beyond. The stalk of the 
gametophore is then a continuation 
of the midrib of the thallus. On 
the apex of this are organized sev- 
eral radial growing points which 
develop the digitate or ray-like 
receptacle. The gametophore is 
thus a specialized branch of the 
thallus. When young, or in many 
cases when nearly or quite mature, 
the gametophore, as one looks at 
the upper surface of the thallus, 
appears to arise from the upper 
surface, as in fig. 261. This is 
because the thin lateral expansions 




Fig. 262. 



Marchantia polymorpha, showing origin of the thallus project forward and 
cf gametophore. overlap in advance of the stalk. It 

is sometimes necessary to tear these overlapping edges apart to see the 
real origin of the gametophore. But in quite old plants these expanded 
portions are farther apart and show clearly that the stalk arises from the 
midrib below and arches upward in the sinus, as in fig. 262. 



CHAPTER XXIV. 

LIVERWORTS CONTINUED. 

488. Sporogonium of marchantia. — If we examine the plant 
shown in fig. 181 we shall see oval bodies which stand out be- 




Fig. 263. 



Archegonial receptacles of marchantia bearing ripe sporogonia. 
psule of the sporogonium projects outside, while the stalk is attac 



The 

attached to 
the receptacle underneath the curtain. In the left figure two of the 
capsules have burst and the elaters and spores are escaping. 

tween the rays of the female receptacle, supported 
on short stalks. These are the sporogonia, or 
spore-cases. We judge at once that they are quite 
different from those which we have studied in 
riccia, since those were not stalked. We can see 
that some of the spore-cases have opened, the wall 
splitting down from the apex in several lines. This 
is caused by the drying of the wall. These tooth- 
like divisions of the wall now curl backward, and 
we can see the yellowish mass of the spores in slow motion, 

231 



232 



MOEPHOLOG Y. 



falling here and there. It appears also as if there were twisting 
threads which aided the spores in becoming freed from the 
capsule. 





Fig. 264. 
Section of archegonial receptacle of Marchantia polymorpha; ripe 
sporogonia. One is open, scattering spores and elaters ; two are 
still enclosed in the wall of the archegonium. The junction of the 
stalk of the sporogonium with the receptacle is the point of attach- 
ment of the sporophyte of marchantia with the gametophyte. 

489. Spores and elaters. — If we take a bit 
of this mass of spores and mount it in water 
for examination with the microscope, we shall 
see that, besides the spores, there are very 
peculiar thread-like bodies, 
the markings of which remind 
one of a twisted rope. These 
are very long cells from the 
inner part of the spore-case, 
and their walls 
are marked by spi- 
ral thickenings. 
This causes them 
in drying, and also 
when they absorb 

Fig. 265. 
moisture, tO tWISt Elater and spore of marchantia. sj>, spore 

and curl in all sporeSj showing partly formed spores - 

sorts of ways. They thus aid in pushing the spores out of the 

capsule as it is drying. 

490. Sporophyte of marchantia compared with riccia. — 
We must recollect that the sporogonium in marchantia is larger 
than in riccia, and that it is also not lying in the tissue of the 
thallus, but is only attached to it at one side by a slender stalk. 




7)ic, mother-cell of 



LIVER WOR TS : MA R CHA NTIA . 



233 



This shows us an increase in the size and complex structure of 
this new phase of the plant, the sporophyte. This is one of the 
very interesting things which we have to note as we go on in the 
study of the higher plants. 




Fig. 266. 
Marchantia polymorpha, archegonium at the left with egg; archegonium at the right with 
young sporogonium ; /, curtain which hangs down around the archegonia ; e, egg ; v, venter 
of archegonium ; n, neck of archegonium ; sj>, young spoiogonium. 

491. Sporophyte dependent on the gametophyte for its nutri- 
ment. — We thus see that at no time during the development of the 
sporogonium is it independent from the gametophyte. This new 
phase of plants then, the sporophyte, has not yet become an in- 
dependent plant, but must rely on the earlier phase for sustenance. 

492. Development of the sporogonium. — It will be interesting to note 
briefly how the development of the marchantia sporogonium differs from that 
of riccia. The first division of the fertilized egg is the same as in riccia, that 
is a wall which runs crosswise of the axis of the archegonium divides it 
into two cells. In marchantia the cell at the base develops the stalk, so 
that here there is a radical difference. The outer cell forms the capsule. 
But here after the wall is formed the inner tissue does not all go to make 
spores, as is the case with riccia. But some of it forms the elaters. While 
in riccia only the outside layer of cells of the sporogonium remained sterile, 
in marchantia the basal half of the egg remains completely sterile and 



234 



MORPHOLOG y. 



develops the stalk, ana in the outer half the part which is formed from some 
of the inner tissue is also sterile. 




Fig. 267. 

Section of developing sporogonia of marchantia ; nt, nutritive tissue of gametophyte ; st, 
sterile tissue of sporophyte ; sj>, fertile part of sporophyte ; va, enlarged venter of arche- 
gonium. 

493. Embryo. — In the development of the embryo we can see all the way 

through this division line between the basal half, which is completely sterile, 

and the outer half, which is the fertile part. In fig. 267 we see a young 

embryo, and it is nearly circular in section although it is composed of 

numerous cells. The basal half is attached to the base of the inner surface 

of the archegonium, and at this time the archegonium still surrounds it. The 

archegonium continues to grow then as the embryo grows, and we can see 

the remains of the shrivelled neck. The portion of the embryo attached to 

the base of the archegonium is the sterile part and is called the " foot," and 

later develops the stalk. The sporogonium during all the stages of its 

development derives its nourishment from the gametophyte at this point of 



LIVERWORTS: MARCHANTIA. 



235 



attachment at the base of the archegonium. Soon, as shown in fig. 267 at 
the right, the outer portion of the sporogonium begins to differentiate into 
the cells which form the elaters and those which form spores. These lie in 
radiating lines side by side, and form what is termed the archesporitwi. Each 
fertile cell forms four spores just as in riccia. They are thus called the 
mother cells of the spores, or spore mother cells. 

494. How marchantia multiplies. — New plants of marchantia are formed 
by the germination of the spores, and growth of the same to the thallus. 
The plants may also be multiplied by parts of the old ones breaking away 
by the action of strong currents of water, and when they lodge in suitable 
places grow into well-formed plants. As the thallus lives from year to year 
and continues to grow and branch the older portions die off, and thus sepa- 
rate plants may be formed from a former single one. 

495. Buds, or gemmae, of marchantia. — But there is another way in which 
marchantia multiplies itself. If we examine the upper surface of such a 




Fig. 268. 
Marchantia plant with cupules and gemmae ; rhizoids below. 

plant as that shown in fig. 268. we shall see that there are minute cup- 
shaped or saucer-shaped vessels, and within them minute green bodies. 
If we examine a few of these minute bodies with the microscope we see that 
they are flattened, biconvex, and at two opposite points on the margin there 
is an indentation similar to that which appears at the growing end of 
the old marchantia thallus. These are the growing points of these little 
buds. When they free themselves from the cups they come to lie on one 



236 



MORPHOLOG V. 



side. It does not matter on what side they lie, for whichever side it is, that 
will develop into the lower side of the thallus, and forms rhizoids, while the 
upper surface will develop the stomates. 



Leafy-stemmed liverworts. 

496. We should now examine more carefully than we have 
done formerly a few of the leafy-stemmed liverworts (called 
foliose liverworts). 

497. Frullania (Fig. 32). — This plant grows on the bark of 
logs, as well as on the bark of standing trees. It lives in quite 

dry situations. 
If we examine 
the leaves we 
will see how it is 
able to do this. 
We note that 
there are two 
rows of lateral 
leaves, which 
are very close 
together, so 
close in fact that 
they overlap 
like the shingles 
on a roof. 
Fi s- 269. Then, as the 

Section of thallus of marchantia. A, through the middle portion ; 
B, through the marginal portion ; /, colorless layer ; chl, chlorophyll Creeping Stems 
layer; s/>, stomate ; h, rhizoids; b, leaf-like outgrowths on under 

side (Goebel). he very close to 

the bark of the tree, these overlapping leaves, which also 
hug close to the stem and bark, serve to retain moisture 
which trickles down the bark during rains. If we examine 
these leaves from the under side as shown in fig. 34, we see 
that the lower or basal part of each one is produced into a 
peculiar lobe which is more or less cup-shaped. This catches 
water and holds it during dry weather, and it also holds moisture 
which the plant absorbs during the night and in damp days. 




FOLIO SE LIVERWORTS. 



237 



There is so much moisture in these little pockets of the under 
side of the leaf that minute animals have found them good places 
to live in, and one frequently discovers them in this retreat. 
There is here also a third row of poorly developed leaves on the 
under side of the stem. 

498. Porella. — Growing in similar situations is the plant known as 
porella. Sometimes there are a few plants 
in a group, and at other times large mats 
occur on the bark of a trunk. This plant, 
porella, also has closely overlapping leaves 
in rows on opposite sides of the stem, and 
the lower margin of each leaf is curved 
under somewhat as 
in frullania, though 
the pocket is not so 
well formed. 

The larger plants 
are female, that is 
they bear archego- 
nia, while the male 
plants, those which 
bear antheridia, are 
smaller and the an- 
theridia are borne 
on small lateral 
branches. The an- 
theridia are borne 
in the axils of the 
leaves. Others of 
the leafy-stemmed 
liverworts live in 
damp situations. 
Some of these, as 
Cephalozia, grow on damp rotten logs. Cephalozia is much more delicate, 
and the leaves are farther apart. It could not live in such dry situations 
where the frullania is sometimes found. If possible the two plants should be 
compared in order to see the adaptation in the structure and form to their 
environment. 




Fig. 270. 
Thallus of a thalloid liverwort (blasia) showing lobed 
margin of the frond, intermediate between thalloid and 
foliose plant. 



499. Sporogonium of a foliose liverwort. — The sporogonium 
of the leafy-stemmed liverworts is well represented by that of 
several genera. We may take for this study the one illustrated 



238 



MORPHOLOG Y. 



in fig. 274, but another will serve the purpose just as -well. We 
note here that it consists of a rounded capsule borne aloft on a 
long stalk, the stalk being much longer proportionately than in 
marchantia. At maturity the capsule splits down into four 





Fig. 272. 
Antheridium of a foliose liverwort (jun 
germannia). 




Fig. 271. 
Foliose liverwort, male plant showing anthe- 
ridia in axils of the leaves (a jungermannia). 



Fig. 273. 
F«liose liverwort, female plant with 
rhizoids. 



quadrants, the wall forming four valves, which spread apart from 
the unequal drying of the cells, so that the spores are set free, as 
shown in fig. 276. Some of the cells inside of the capsule de- 
velop elaters here also as well as spores. These are illustrated 
in fig. 278. 

500. In this plant we see that the sporophyte remains attached 



FOLIO SE LIVERWORTS. 



239 



to the gametophyte, and thus is dependent on it for sustenance. 
This is true of all the plants of this 
group. The sporophyte never becomes 
capable of an independent existence, 
and yet we see that it is becoming 
larger and more highly differentiated 
than in the simple riccia. 




Fig. 275. 

Opening capsule 
showing escape of 
spores and elaters. 




Capsule parted down 
to the stalk. 





Fig. 274- 

Fruiting plant of a foliose liver- ¥is. 277. Fig. 278. 
wort (jungermannia). Leafy part 

is the gametophyte ; stalk and cap- Four spores from Elaters, at left showing the two 

sule is the sporophyte (sporogonium mother cell held in spiral marks, at right a branched 

in the bryophytes). a group. elater. 

Figs. 275-278. — Sporogonium of liverwort (jungermannia) opening by splitting into four 
parts, showing details of elaters and spores. 



240 



MORPHOLOGY. 



The Horned Liverworts.* 

501. The horned liverworts take their name from the shape of the spo- 
rogonium. This is long, slender, cylindrical, pointed, and very slightly 
curved, suggesting the shape of a minute horn. Anthoceros is one of the 
most common and widely distributed species. The plant grows on damp 
soil or on mud. 

Anthoceros. 

502. The gametophyte. — The gametophyte is thalloid. It is thin, flat- 
tened, green, irregularly ribbon-shaped and branched. It lies on the soil 

and is more or less crisped or 
wavy, or curled, the edges nearly 
plane, or somewhat irregular, 
and with minute lobes, or 
notches, especially near the 
growing end. The general form 
and branching can be seen in 
fig. 279. Where the plants are 
much crowded the thallus is more 
irregular, and often possesses nu- 
merous small lateral branches in 
addition to the main lobes. 
Upon the under side are the 
slender rhizoids, which attach 
to the soil. With a hand lens 
there can be seen also upon the 
under side small dark, rounded 
and thickened spots, where an 
alga (nostoc) is located. 

Sexual Organs of 

Anthoceros. 
502. The sexual organs of an- 
thoceros differ considerably from 
those of the other liverworts 




F 

Fig. 279. 
Anthoceros gracilis. A, several gameto 
phytes, on which sporangia have developed, 
B, an enlarged sporogonium, showing its studied. In the first place they 
elongated character and dehiscence by two 
valves, leaving exposed the slender columell 



are immersed in the true tissue 



on the surface of which are the spores, C, D, f the Callus, i.e., thev do not 

E, F, elaters of various forms, G-, spores. 

(After Schiffner.) project above the surface. 

503. Antheridia. — The antheridium arises from an internal cell of the 

thallus, a cell just below the upper surface. This cell develops usually a 



May be used as an alternate study for marchantia. 



HORNED LIVERWORTS. 24 1 

group of antheridia which lie in a cavity formed around this cell as the 
thallus continues to grow. They are situated along the middle line of the 
thallus, and can be seen by making a section in this direction. The anthe- 
ridia are oval or rounded, have a wall of one layer of cells which contains 
the sperm cells, and each antheridium has a slender stalk. The sperms 
are like those of the true liverworts. 

504. Archegonia. — The archegonia are also borne along the middle line 
of the thallus. Each one arises at an early stage in the development of 
the tissue of the thallus from a superficial cell, but the archegonium does 
not project above the surface. The venter therefore which contains the 
egg is deep down in the thallus, the wall of the neck is formed from cells 
indistinguishable from the adjoining cells of the thallus and opens at the 
surface. 

Sporophyte of Anthoceros. 

505. The Sporogonium. — The sporogonium is developed from the fer- 
tilized egg, fertilization resulting of course from the fusion of one of the 
sperms with the nucleus of the egg. From the lower part of the embryo 
certain cells elongate and push out like rhizoids into the thallus (gameto- 
phyte), but never reach the outside so that the sporogonium derives its 
nutriment from the gametophyte in a parasitic manner like the true liver- 
worts. It is surrounded at the base by a sheath, an outgrowth of the 
gametophyte. 

506. Growing point of the sporogonium. — A remarkable thing about 
the sporogonium of anthoceros, and its relatives, is that the growing point 
instead of being situated at the free end is located near the base, just above 
the nourishing foot. Thus the upper part of the sporogonium is older. In 
the old sporogonia there may be ripe spores near the free end, young ones 
near the middle, and undifferentiated growing tissue near the base. A 
longitudinal section of a sporogonium just as the spores are ripening will 
show this. 

507. Structure of the sporogonium. — A longitudinal section of the spo- 
rogonium shows that the spore-bearing tissue occupies a comparativelv 
small portion of the sporogonium. In the section there is a narrow laver 
(two cells thick) on either side and joined at the top. In the entire spo- 
rogonium this fertile tissue is in the shape of an inverted test-tube situated 
inside of the sporogonium. The wall of the sporogonium is about four 
cells thick. The sterile tissue inside of the spore-bearing tube is the colu- 
mella. The cells of the wall contain chlorophyll, and there are true stomata 
with guard cells in the epidermal layer. 

508. Spores and elaters. — In the spore-bearing tissue there are two layers 
of cells (the archesporium) . Each cell is a potential mother-cell. The 
cells, however, of alternate tiers do not form spores. They elongate some- 



242 MORPIWLOG V. 

what and are somewhat irregular and sometimes divide or branch. They 
are supposed to represent rudimentary elaters. The cells in the other tiers 
are actual mother-cells, and each one forms four spores. 

509. The sporophyte of anthoceros represents the highest type found in 
the liverworts. The spongy green parenchyma forming the wall, with the 
stomata in the epidermal layer, fits this tissue for the process of photosyn- 
thesis, so that this part of the sporophyte functions as the green leaf of the 
seed plants. It has been suggested by some that if the rhizoids on the 
nourishing foot could only extend outside and anchor in the soil, the sporo- 
phyte of anthoceros could live an independent existence. But we see that 
it stops short of that. 

Classification of the Liverworts. 

CLASS HEPATICiE. 

510. Order Marchantiales.* — There are two families represented in 
the United States. 

Family Ricciacese, including Riccia and Ricciocarpus. 
Family Marchantiaceae, including Marchantia, Fegatella (= Cono- 
cephalus), Fimbriaria, Targionia, etc. 

511. Order Jungermanniales * — There are two subdivisions of this order. 
The Anacrogynce. include chiefly thalloid forms with continued apical 
growth, the archegonia back of the apical cell. Examples: Blasia, Aneura, 
Pellia, etc. 

The Acrogynce include chiefly foliose forms, the archegonia arising from 
the apical cell and in such cases interrupting apical growth. Examples: 
Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium, Porella, etc. 

CLASS ANTHOCEROTES. 

512. The Anthocerotes have formerly been placed with the Hepaticae 
as an order. But because of their wide divergence from the other liver- 
worts in the development of the sexual organs, and especially in the struc- 
ture of the sporophyte, they are now by some separated as a distinct class. 
There is one order. 

Order Anthocerotales * — This includes one family (Anthocerotaceae) 
with Anthoceros and Notothylas in Europe and North America, and Den- 
droceros in the tropics. The latter is epiphytic. 



* As subclass in Engler and Prantl. 



CHAPTER XXV. 

MOSSES (MUSCI). 

513. We are now ready to take up the more careful study of 
the moss plant. There are a great many kinds of mosses, and 
they differ greatly from each other in the finer details of struc- 
ture. Yet there are certain general resemblances which make it 
convenient to take for study almost any one of the common 
species in a neighborhood, which forms abundant fruit. Some, 
however, are more suited to a first study than others. (Polytri- 
chum and funaria are good mosses to study.) 

514. Mnium.— We will select here the plant shown in fig. 280. 
This is known as a mnium (M. affine), and one or another of the 
species of mnium can be obtained without much difficulty. 
The mosses, as we have already learned, possess an axis 
(stem) and leaf-like expansions, so that they are leafy-stemmed 
plants also. Certain of the branches of the mnium stand upright, 
or nearly so, and the leaves are all of the same size at any given 
point on the stem, as seen in the figure. There are three rows 
of these leaves, and this is true of most of the mosses. 

515. The mnium plants usually form quite extensive and pretty 
mats of green in shady moist woods or ravines. Here and there 
among the erect stems are prostrate ones, with two rows of promi- 
nent leaves so arranged that it reminds one of some of the leafy- 
stemmed liverworts. If we examine some of the leaves of the 
mnium we see that the greater part of the leaf consists of a 
single layer of green cells, just as is the case in the leafy -stemmed 
liverworts. But along the middle line is a thicker layer, so that 
it forms a distinct midrib. This is characteristic of the leaves 

343 



244 



MORPHOLOGY. 



of mosses, and is one way in which they are separated from the 
leafy-stemmed liverworts, the latter never having a midrib. 

516. The fruiting moss plant. — In fig. 280 is a moss plant " in 
fruit," as we say. Above the leafy stem a slender stalk bears 





the capsule, and in this capsule are borne 
the spores. The capsule then belongs to 
the sporophyte phase of the moss plant, and 
we should inquire whether the entire plant 
as we see it here is the sporophyte, or 
whether part of it is gametophyte. If 
a part of it is gametophyte and a part 
sporophyte, then where does the one end 
and the other begin ? If we strip off the 
leaves at the end of the leafy stem, and 
make a longisection in the middle line, we 
should find that the stalk which bears the 
capsule is simply stuck into the end of the 



Fig. 280. 

Portion of moss plant of Mnium affine, showing two 
sporogonia from one branch. Capsule at left has just shed 
the cap or operculum ; capsule at right is shedding spores, 
and the teeth are bristling at the mouth. Next to the right 
is a young capsule with calyptra still attached ; next are 
two spores enlarged. 



leafy stem, and is not organically connected with it. This is 
the dividing line, then, between the gametophyte and the sporo- 
phyte. We shall find that here the archegonium containing 



MOSSES. 



245 



the egg is borne, which is a surer way of determining the limits 
of the two phases of the plant. 

517. The male and female moss plants. — The two plants of mnium shown in 
figs. 281, 282 are quite different, as one can easily see, and yet they belong 
to the same species. One is a female plant, while the other is a male plant. 

The sexual organs then in mnium, as 
in many others of the mosses, are borne 
on separate plants. The archegonia 
are borne at the end of the stem, and are 
protected by somewhat narrower leaves 
which closely overlap and are wrapped 
together. They are similar to the 
archegonia of the liverworts. 





Fig. 281. 
Female plant (gametophyte) of a moss 
(mnium), showing rhizoids below, and the 
tuft of leaves above which protect the arche- 
gonia. 



Fig. 282. 
Male plant (gametophyte) of a moss 
(mnium) showing rhizoids below and the 
antheridia at the center above surrounded by 
the rosette of leaves. 



The male plants of mnium are easily selected, since the leaves at the end 
of the stem form a broad rosette with the antheridia, and some sterile threads 
packed closely together in the center. The ends of the mass of antheridia 
can be seen with the naked eye, as shown in fig. 282. When the antheridia 



246 



MORPHOLOG Y. 



are ripe, if we make a section through a cluster, or if we merely tease out 
some from the end with a needle in a drop of water on the slide, then prepare 
for examination with the microscope, we can see the form of the antheridia. 
They are somewhat clavate or elliptical in outline, as seen in fig. 284. Be- 
tween them there stand short threads composed of several cells containing 
chlorophyll grains. These are sterile threads (paraphyses). 

518. Sporogonium. — In fig. 280 we see illustrated a sporogonium of mnium, 
which is of course developed from the fertilized egg cell of the archegonium. 
There is a nearly cylindrical capsule, bent downward, and supported on a lon^ 




Fig. 284. 

Fig. 283. Antheridium of milium 

Section through end of stem of female plant of mnium, show- with jointed paraphysis 
ing archegonia at the center. One archegonium shows the egg. at the left ; spermato- 
On the sides are sections of the protecting leaves. zoids at the right. 

slender stalk. Upon the capsule is a peculiar cap,* shaped like a ladle or 
spatula. This is the remnant of the old archegonium, which, for a time sur- 
rounded and protected the young embryo of the sporogonium, just as takes 
place in the liverworts. In most of the mosses this old remnant of the arche- 
gonium is borne aloft on the capsule as a cap, while in the liverworts it is 
thrown to one side as the sporogonium elongates. 
519. Structure of the moss capsule. — At the free end on the moss capsule 



* Called the calyptra. 



MOSSES. 



247 



as shown in the case of mnium in fig. 280, after the remnant of the arche- 

gonium falls away, there is seen a conical lid which fits closely over the end. 

When the capsule is ripe this lid easily falls away, and can be brushed off 

so that it is necessary to handle the plants with care if it is 

desired to preserve this for study. 

520. When the lid is brushed away as the capsule dries 
more we see that the end of the capsule covered by the lid 
ippears "frazzled." If we examine this end with the micro- 
scope we see that the tissue of the capsule here is torn 
with great regularity, so that there are two rows of narrow, 
sharp teeth which project outward in a ring around the 
opening. If we blow our "breath" upon these teeth they 
will be seen to move, and as the 
moisture disappears and reappears 
in the teeth, they close and open 
the mouth of the. capsule, so sensi- 
tive are they to the changes in the 
humidity of the air. In this way 
all of the spores are prevented to 
some extent from escaping from 
the capsule at one time. 

521. Note. If we make a sec- 
tion longitudinal of the capsule of 
mnium, or some other moss, we find 
that the tissue which develops the 
spores is much more restricted 
than in the capsule of the liver- 
Worts which we have studied. The 
spore -bearing tissue is confined to 
a single layer which extends around 
the capsule some distance from the 
outside of the wall, so that a central 

Two different stages of young sporogonium of cylinder is left of sterile tissue, 
a moss, still within the archegonium and wedg- This is the columella, and is pres- 
mg their way into the tissue ot the end ot the stem. r 

h, neck of archegonium ; /, young sporogonium. ent in nearly all the mosses. Each 
This shows well the connection of the sporophyte . ,, ,, , ,, r ... , 

with the gametophyte. of the cells of the fertile layer 

divides into four spores. 

522. Development ol the sporogonium. — The egg cell after fertilization 

divides by a wall crosswise to the axis of the archegonium. Each of these 

cells continues to divide for a time, so that a cylinder pointed at both ends is 

formed. The lower end of this cylinder of tissue wedges its way down 

through the base of the archegonium into the tissue of the end of the moss 

stem as shown in fig. 285. This forms the foot through which the nutrient 





Fig. 285. 



248 MORPHOLOGY. 

materials are passed from the gametophyte to the sporogonium. The upper 
part continues to grow, and finally the upper end differentiates into the mature 
capsule. 

523. Protonema of the moss. — When the spores of a moss germinate they 
form a thread-like body, with chlorophyll. This thread becomes branched, 
and sometimes quite extended tangles of these threads are formed. This is 
called the protonema, that is first thread. The older threads become finally 
brown, while the later ones are green. From this protonema at certain 
points buds appear which divide by close oblique walls. From these buds 
the leafy stem of the moss plant grows. Tiireads similar to these protonemal 
threads now grow out from the leafy stem, to form the rhizoids. These 
supply the moss plant with nutriment, and now the protonema usually dies, 
though in some few species it persists for long periods. 

Classification of the Mosses. 

CLASS MUSCINEJE (MUSCI). 

524. Order Sphagnales * — This order includes the peat mosses. There 
is but one family (Sphagnaceae) and but a single genus (Sphagnum). The 
peat mosses are widely distributed over the globe, chiefly occurring in 
moors, or "bogs," usually low ground around the shores of lakes, ponds, or 
along streams, but they often occur on wet dripping rocks in cool shady 
places. Small ponds are sometimes filled in by their growth. As the 
sphagnum growing in such an abundance of water only partially decays, 
' ' ground ' ' is built up rather rapidly, and the sphagnum remains are known 
as "peat." This "ground "-building peculiarity of sphagnum sometimes 
enables the plant (often in conjunction with others) to fill in ponds com- 
pletely. (See Atoll Moor, Chapter LV.) 

The gametophyte of sphagnum, like that of all the mosses, is dimorphic, 
but the first part (or protonema) which develops from the spores is thalloid, 
and therefore more like the thallose liverworts. The leafy axis (or gameto- 
phore) which develops from the thalloid form is very characteristic (see 
Chapter LV). 

The archegonia are borne on the free end of the main axis, while the 
antheridia are borne on short branches which are brightly colored, red, 
yellow, etc. The sporophyte (sporogonium) is globose and possesses a 
broad foot anchored in the end of a naked prolongation of the end of the 
leafy gametophore. This naked prolongation of the gametophore looks 
like the stalk of the sporogonium, but a study of its connection with the 
sporogonium shows that it is part of the gametophyte, which is only devel- 
oped after the fertilization of the egg in the archegonium. In the sporogo- 
nium there is a short columella, and the archesporium is in the form of an 
inverted cup. 



* As subclass in Fngler and Prantl. 



MOSSES. 249 

525. Order Andreaeales* — This order includes the single genus An- 
dreaea. The plants are small but form extensive mats, growing on rocks 
in arctic or alpine regions usually. They are sometimes found in great 
abundance on bare, rather dry rocks on mountains. The protonema is 
somewhat thalloid. The sporogonium opens by splitting longitudinally into 
four valves. An elongated columella is present so that the archesporium 
is shaped like an inverted test-tube. 

526. Order Archidiales* — This order contains the single genus Archi- 
dium, and by some is placed as an aberrant genus in the Bryales. There 
is no columella in the simple sporogonium. The archesporium occupies 
all the internal part of the sporogonium, some cells being fertile and others 
sterile. 

527. Order Bryales.* — These include the higher mosses, and a very large 
number of genera and species. The protonema is filamentous and branched 
except in a few forms where it is partly thalloid as in Tetraphis (= Georgia). 
(Tetraphis pellucida is a common moss on very rotten logs. The 
capsule has four prominent teeth.) In a few of the lower genera (Phas- 
cum, Pleuridium, etc.) the capsule opens irregularly, but in the larger num- 
ber the capsule opens by a lid (operculum). A cylindrical columella is 
present, and the archesporium is in the form of a tube open at both ends. 
(Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.) 



* As subclass in Engler and Prantl. 



250 



MORPHOLOG Y. 



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CHAPTER XXVI. 
FERNS. 

529. In taking up the study of the ferns we find plants which 
are very beautiful objects of nature and thus have always attracted 
the interest of those who love the beauties of nature. But they 
are also very interesting to the student, because of certain re- 
markable peculiarities of the structure of the fruit bodies, and 
especially because of the inteimediate position which they occupy 
within the plant kingdom, representing in the two phases of 
their development the primitive type of plant life on the one 
hand, and on the other the modern type. We will begin our 
study of the ferns by taking that form which is the more promi- 
nent, the fern plant itself. 

530. The Christmas fern. — One of the ferns which is very 
common in the Northern States, and occurs in rocky banks and 
woods, is the well-known Christmas fern (Aspidium acrostichoides) 
shown in fig. 286. The leaves are the most prominent part of the 
plant, as is the case with most if not all our native ferns. The 
stem is very short and for the most part under the surface of the 
ground, while the leaves arise very close together, and thus form 
a rosette as they rise and gracefully bend outward. The leaf is 
elongate and reminds one somewhat of a plume with the pinnae 
extending in two rows on opposite sides of the midrib. These 
pinnae alternate with one another, and at the base of each pinna 
is a little spur which projects upward from the upper edge. 
Such a leaf is said to be pinnate. While all the leaves have the 
same general outline, we notice that certain ones, especially those 
toward the center of the rosette, are much narrower from the 

25 1 



252 



MORPHOLOG Y. 



middle portion toward the end. This is because of the shorter 
pinnae here. 

531. Fruit "dots" (sorus, indusium). — If we examine the 
under side of such short pinnae of the Christmas fern we see that 
there are two rows of small circular dots, one row on either side of 
the pinna. These are called the "fruit 
dots," or sori (a single one is a sorus). If 
we examine it with a low power of the mi- 
croscope, 
or with a 
p o c k e t 
lens, we 
see that 
there is a 
ci re ular 
disk which 
c o vers 
more or 
less com- 
pletelyvery 
minute objects, usual- 
ly the ends of the 
latter projecting just be- 
yond the edge if they are 
mature. This circular disk 
is what is called the indu- 
sium, and it is a special 
outgrowth of the epidermis 
of the leaf here for the 
protection of the spore- 
cases. These minute ob- 
jects underneath are the 
fruit bodies, which in the 
case of the ferns and their allies are called sporangia. This 
indusium in the case of the Christmas fern, and also in some 
Others, is attached to the leaf by means of a short slender stalk 




Fig. 286. 
Christmas fern (Aspidium acrostichoides). 



FERNS. 



253 



which is fastened to the middle of the under side of this shield, 

as seen in cross section in fig. 292. 

532. Sporangia.— If we section through the leaf at one of the 

fruit dots, or if we tease off some of the sporangia so that the 

stalks are still attached, and 
examine them with the mi- 
croscope, we can see the 
form and structure of these 
peculiar bodies. Different 
views of a sporangium are 
shown in fig. 293. The 
slender portion is the stalk, 
and the larger part is the 
spore-case proper. We 
should examine the structure 
of this spore-case quite care- 
fully, since it will help us to 
understand better than we 
otherwise could the remark- 
able operations which it 
performs in scattering the 
spores. 

533. Structure of a spo- 
rangium. — If we examine 
one of the sporangia in side 
view as shown in fig. 293, 
Fig. 287. we note a prominent row of 

Rhizome with bases of leaves, and roots of the ce H s which extend around 
Christmas fern. 

the margin of the dorsal 
edge from near the attachment of the stalk to the upper front 
angle. The cells are prominent because of the thick inner 
walls, and the thick radial walls which are perpendicular to the 
inner walls. The walls on the back of this row and on its 
sides are very thin and membranous. We should make this 
out carefully, for the structure of these cells is especially adapt- 
ed to a special function which they perform. This row of cells 




254 



MORPHOLOG V. 



is termed the annu/us, which means a little ring. .While this 
is not a complete ring, in some other ferns the ring is nearly 
complete. 

534. In the front of the sporangium is another peculiar group 




Rhizome of sensitive fern (Onoclea sensibilis). 

of cells. Two of the longer ones resemble the lips of some crea- 
ture, and since the sporangium opens between them they are 
sometimes termed the lip cells. These lip cells are connected with 
the upper end of the annulus on one 
side and with the upper end of the stalk 
on the other side by thin -walled cells, 
which may be termed connective cells, 
since they hold each lip cell to its part 
of the opening sporangium. The cells 
on the side of the sporangium are also 
thin -walled. If we now examine a 
sporangium from the back, or dorsal 
Under side of pinna'of Aspidium edge as we say, it will appear as in the 

spinulosum showing fruit dots . - . . ~ TT 

(sori). left-hand figure. Here we can see 

how very prominent the annulus is. It projects beyond the 
surface of the other cells of the sporangium. The spores are 
contained inside this case. 




Fig. 



oil I LUST 



FERNS. 



W 



535. Opening of the sporangium and dispersion of the 
spores. — If we take some fresh fruiting leaves of the Christmas 
fern, or of any one of many of the species of the true ferns just 
at the ripening of the spores, and place a portion of it on a piece 
of white paper in a dry room, in a very short time we shall see 
that the paper is being dusted with minute brown objects which 
fly out from the leaf. Now if we take a portion of the same 
leaf and place it under the low power of the microscope, so that 
the full rounded sporangia can be seen, in a short time we note 
that the sporangium opens, the upper half curls backward as 




Fig. 290. 
Four pinnae of adiantum, showing recurved margins which cover the sporangia. 

shown in fig. 294, and soon it snaps quickly, to near its former 
position, and the spores are at the same time thrown for a consid- 
erable distance. This movement can sometimes be seen with the 
aid of a good hand lens. 

536. How does this opening and snapping of the sporan- 
gium take place ? — We are now more curious than ever to see 
just how this opening and snapping of the sporangium takes place. 
We should now mount some of the fresh sporangia in water and 
cover with a cover glass for microscopic examination. A drop 
of glycerine should be placed at one side of the cover glass on the 
slip so that the edge of the glycerine will come in touch with the 
water. Now as one looks through the microscope to watch the 



256 



MORPHOLOGY. 



sporangia, the water should be drawn from under the cover glass 
with the aid of some bibulous paper, like filter paper, placed at the 

edge of the cover glass on 
the opposite side from the 
glycerine. As the glycer- 
ine takes the place of the 
water around the sporangia 
it draws the water out of 
the cells of the annulus, 
just as it took the water 
out of the cells of the 
spirogyra as we learned 
some time ago. As the 
water is drawn out of these 
cells there is produced a 
pressure from without, the 
atmospheric pressure upon 
the glycerine. This causes 
the walls of these cells of 
the annulus to bend in- 
ward, because, as we have 
already learned, the glycer- 

Section through sorus of Polypodium vulgare -[ ne does not pass thrOUffh 
showing different stages of sporangium, and one L ° 

multicellular capitate hair. fa e wa U s near ly so f ast 

as the water comes out. 

537. Now the structure of the cells of this annulus, as we 
have seen, is such that the inner walls and the perpendicular 





Fig. 292. 
Section through sorus and shield-shaped indusium of aspidium. 

walls are stout, and consequently they do not bend or collapse 
when this pressure is brought to bear on the outside of the cells. 



FERNS. 



2?7 



The thin membranous walls on the back (dorsal walls) and on 
the sides of the annulus, however, yield readily to the pressure 
and bend inward. This, as we can readily see, pulls on the ends 
of each of the perpendicular walls drawing them closer together. 
This shortens the outer surface of the annulus and causes it to 
first assume a nearly straight position, then curve backward until 
it quite or nearly becomes doubled on itself. The sporangium 




Fig. 293. 
Rear, side, and front views of fern sporangium, d, e, annulus; a, lip cells. 

opens between the lip cells on the front and the lateral walls of 
the sporangium are torn directly across. The greater mass of 
spores are thus held in the upper end of the open sporangium, 
and when the annulus has nearly doubled on itself it suddenly 
snaps back again in position. While treating with the glycerine 
we can see all this movement take place. Each cell of the 
annulus acts independently, but often they all act in concert. 
When they do not all act in concert, some of them snap sooner 
than others, and this causes the annulus to snap in segments. 

538. The movements of the sporangium can take place in 
old and dried material. — If we have no fresh material to study 



258 



MORPHOLOGY. 



the sporangium with, we can use dried material, for the move- 
ments of the sporangia can be well seen in dried material, pro- 
vided it was collected at about the time the sporangia are mature, 
that is at maturity, or soon afterward. We take some of the 
dry sporangia (or we may wash the glycerine off those which we 
have just studied) and mount them in water, and quickly examine 




Q=^ 



^TS&X^^ 1 







0'\ \\\\& 

\\ »\ v, ^ \~±*\ 



Fig. 294. 
Dispersion of spores from sporangium of Aspidium acrostichoides, showing different 
stages in the opening and snapping of the annulus. 

them with a microscope. We notice that in each cell of the 
annulus there is a small sphere of some gas. The water which 
bathes the walls of the aimulus is absorbed by some substance 
inside these cells. This we can see because of the fact that this 
sphere of gas becomes smaller and smaller until it is only a mere 



FEXNS. 259 

dot, when it disappears in a twinkling. The water has been taken 
in under such pressure that it has absorbed all the gas, and the 
farther pressure in most cases closes the partly opened sporangium 
more completely. 

539. Now we should add glycerine again and draw out the 
water, watching the sporangia at the same time. We see that 
the sporangia which have opened and snapped once will do it 
again. And so they may be made to go through this operation 
several times in succession. We should now note carefully the 
annulus, that is after the sporangia have opened by the use of 
glycerine. So soon as they have snapped in the glycerine we can 
see those minute spheres of gas again, and since there was no air 
on the outside of the sporangia, but only glycerine, this gas must, 
it is reasoned, have been given up by the water before it was all 
drawn out of the cells. 

540. The common polypody. — We may now take up a few other ferns for 
study. Another common fern is the polypody, one or more species of which 
have a very wide distribution. The stem of this fern is also not usually seen, 
but is covered with the leaves, except in the case of those species which grow 
on the surface of rocks. The stem is slender and prostrate, and is covered 
with numerous brown scales. The leaves are pinnate in this fern also, but we 
find no difference between the fertile and sterile leaves (except in some rare 
cases). The fruit-dots occupy much the same positions on the under side of the 
leaf that they do in the Christmas fern, but we cannot find any indusium. In 
the place of an indusium are club-shaped hairs as shown in fig. 291. The en- 
larged ends of these clubs reaching beyond the sporangia give some protection 
to them when they are young. 

541. Other ferns. — We might examine a series of ferns to see how different 
they are in respect to the position which the fruit dots occupy on the leaf. The 
common brake, which sometimes covers extensive areas and becomes a trouble- 
some weed, has a stout and smooth underground stem (rhizome) which is often 
12 to 20 cm beneath the surface of the soil. There is a long leaf stalk, which 
bears the lamina, the latter being several times pinnate. The margins of the 
fertile pinnae are inrolled, and the sporangia are found protected underneath 
in this long sorus along the margin of the pinna. The beautiful maidenhair fern 
and its relatives have obovate pinnae, and the sori are situated in the same posi- 
tions as in the brake. In other ferns, as the walking fern, the sori are borne 
along by the side of the veins of the leaf. 

542. Opening of the leaves of ferns. — The leaves of ferns open in a peculiar 
manner. The tip of the leaf is the last portion developed, and the growing 



26o 



MORPHOLOG Y. 



leaf appears as if it was rolled up as in fig. 287 of the Christmas fern. As the 
leaf elongates this portion unrolls. 

543. Longevity of ferns. — Most ferns live from year to year, by growth 
adding to the advance of the stem, while by decay of the older parts the stem 
shortens up behind. The leaves are short-lived, usually dying down each 
year, and a new set arising from the growing end of the stem. Often one can 
see just back or below the new leaves the old dead ones of the past season, 
and farther back the remains of the petioles of still older leaves. 

544. Budding of ferns. — A few 
ferns produce what are called bulbils 
or bulblets on the leaves. One of 
these, which is found throughout the 
greater part of the eastern United 
States, is the bladder fern (Cystop- 
teris bulbifera), which grows in shady 
rocky places. The long graceful 
delicate leaves form in the axils of 
./A the pinnae, especially near the end of 
■ the leaf, small oval bulbs as shown 
in fig. 295. If we examine one of 
these bladder-like bulbs we see that 
the bulk of it is made up of short 
thick fleshy leaves, smaller ones ap- 
pearing between the outer ones at the 
smaller end of the bulb. This bulb 
contains a stem, young root, and 
several pairs of these fleshy leaves. 
They easily fall to the ground or 
rocks, where, with the abundant 
moisture usually present in localities 

where the fern is found, the bulb 
Fig. 2Q5- . ' 

Cvstopteris bulbifera, young plant growing grows until the roots attach the plant 
from bulb. At right is young bulb in axil of to the soil or in the crev i ce s of the 
pinna 01 leaf. 

rocks. A young plant growing from 

one of these bulbils is shown in fig. 295. 

545. Greenhouse ferns. — Some of the ferns grown in conservatories have 
similar bulblets. Fig. 296 represents one of these which is found abundantly 
on the leaves of Asplenium bulbiferum. These bulbils have leaves which are 
very similar to the ordinary leaf except that they are smaller. The 
bulbs are also much more firmly attached to the leaf, so that they do not 
readily fall away. 

546. Plant conservatories usually furnish a number of very interesting 
ferns, and one should attempt to make the acquaintance of some of them, for 




FERNS. 



26l 



here one has an opportunity during the winter season not only to observe these 
interesting plants, but also to obtain material for study. In the tree ierns 
which often are seen growing in such places we see examples of the massive 
trunks and leaves of some of the tropical species. 

547. The fern plant is a sporophyte. — We have now studied 
the fern plant, as we call it, and we have found it to represent 
the spore-bearing phase of the plant, that is the sporophyte (cor- 
responding to the sporogonium of the liverworts and mosses). 

548. Is there a ga- 
in etophyte phase in 
ferns ? — But in the spor- 
ophyte of the fern, which 
we should not forget is 
the fern plant, we have 
a striking advance upon 
the sporophyte of the 
liverworts and mosses. 
In the latter plants the 
sporophyte remained 
attached to the gameto- 
phyte, and derived its 
nourishment from it. 
In the ferns, as we see, 
the sporophyte has a 
root of its own, and is 
attached' to the soil. 
Through the aid of root 

hairs of its own it takes up mineral solutions. It possesses also 
a true stem, and true leaves in which carbon conversion takes 
place. It is able to live independently, then. Does a gametophyte 
phase exist among the ferns ? Or has it been lost ? If it does 
exist, what is it like, and where does it grow? From what we 
have already learned we should expect to find the gametophyte 
begin with the germination of the spores which are developed 
on the sporophyte, that is on the fern plant itself. We should 
investigate this and see. 




Fig. 296. 

Bulbil growing from leaf of asplenium {A, bulbiferum). 



CHAPTER XXVII. 

FERNS CONTINUED. 

Gametophyte of ferns. 

549. Sexual stage of ferns. — We now wish to see what the 
sexual stage of the ferns is like. Judging from what Ave have 
found to take place in the liverworts and mosses we should infer 




Fig. 297. 
Prothallium of fern, under side, showing rhizoids, antheridia scattered among and near 
them, and the archegonia near the sinus. 

that the form of the plant which bears the sexual organs is de- 
veloped from the spores. This is true, and if we should examine 
pld decaying logs, or decaying woo4 in damp places in the near 



FEKNS. 



26S 




Fig. 298. 
Spore of Pteris serru- 
lata showing the three- 
rayed elevation along 
the side of which the 
spore wall cracks during 
germination. 



vicinity of ferns, we should probably find tiny, green, thin, heart- 
shaped growths, lying close to the substratum. These are also 
found quite frequently on the soil of pots in plant conservatories 
where ferns are grown. Gardeners also in conservatories usually 
sow fern spores to raise new fern plants, 
and usually one can find these heart-shaped 
growths on the surface of the soil where 
they have sown the spores. We may call 
the gardener to our aid in finding them in 
conservatories, or even in growing them for 
us if we cannot find them outside. In some 
cases they may be grown in an ordinary room 
by keeping the surfaces where they are 
growing moist, and the air also moist, by 
placing a glass bell jar over them. 

550. In fig. 297 is shown one of these growths enlarged. 
Upon the under side we see numerous thread-like outgrowths, 
the rhizoids, which attach the plant to the substratum, and which 
act as organs for the absorption of nourishment. The sexual 

organs are 
borne on the 
under side also, 
and we will 
study them 
later. This 
heart-shaped, 
flattened, thin, 
green plant is 
the prothalliwn 

of ferns, and we should now give it more careful study, be-. 

ginning with the germination of the spores. 

551. Spores. — We can easily obtain material for the study of 
the spores of ferns. The spores vary in shape to some extent. 
Many of them are shaped like a three-sided pyramid. One of 
these is shown in fig. 298. The outer wall is roughened, and 
on one end are three elevated ridges which radiate from a given 




Fig. 299 



Spore of Aspidium 
acrostichoides with 
winged exospore. 



Fig. 300. 

Spore crushed to remove exospore and 
show endospore. 



264 



MORPHOLOG Y. 




Fig. 30 r. 
Spores of asplenium ; exospore re 
moved from the one at the right. 



point. A spore of the Christmas fern is shown in fig. 299. The 
outer wall here is more or less winged. At fig. 300 is a spore 

of the same species from which the 
outer wall has been crushed, showing 
that there is an inner wall also. If 
possible we should study the germi- 
nation of the spores of some fern. 

552. Germination of the spores. 
— After the spores have been sown for 
about one week to ten days we should 
mount a few in water for examination 
with the microscope in order to study 
the early stages. If germination has begun, we find that here 
and there are short slender green threads, in many cases attached 

to brownish bits, the old 
walls of the spores. 
Often one will sow the 
sporangia along with the 
spores, and in such cases 
there may be found a 
number of spores still 
within the old sporan- 
gium wall that are ger- 
minating, when they will 
appear as in fig. 302. 

553. Pr-otonema. — 
These short green threads 
are called protonemal threads, or protonema, 
which means a first thread, and it here 
signifies that this short thread only pre- 
cedes a larger growth of the same object. 
In figs. 302, 303 are shown several stages of 
germination of different spores. Soon after 
Germina F tSg 3 °spores of the short germ tube emerges from the 
s P p t oran g lum lina StU1 m the crack in the spore wall, it divides by the 





FERNS. 265 

formation of a cross wall, and as it increases in length other 
cross walls are formed. But very early in its growth we see that 
a slender outgrowth takes place from the cell nearest the old 
spore wall. This slender thread 
is colorless, and is not divided 
into cells. It is the first rhizoid, 
and serves both as an organ of 
attachment for the thread, and for 
taking up nutriment. 

554. Prothallium. — Very soon, 
if the sowing has not been so 
crowded as to prevent the young 
plants from obtaining nutriment 
sufficient, we will see that the end 
of this protonema is broadening, 
as shown in fig. 303. This is done 
by the formation of the cell walls 
in different directions. It now 
continues to grow in this way, the 
end becoming broader and broader, 
and new rhizoids are formed from 
the under surface of the cells. The 
growing point remains at the mid- 
dle of the advancing margin, and 
the cells which are cut off from 
either side, as they become old, 
widen out. In this way the v fl ir g ' 3 ° 3 ' f t ( • 1 

J \ oung prothallium of a fern (nipho- 

" wings," or margins of the bolus )- 

little, green, flattened body, are in advance of the growing 

point, and the object is more or less heart-shaped, as shown 

in fig. 297. Thus we see how the prothallium of ferns is 

formed. 

555. Sexual organs of ferns. — If we take one of the prothal- 
lia of ferns which have grown from the sowings of fern spores, 
or one of those which may be often found growing on the soil 




266 



MORPHOLOG Y. 



of pots in conservatories, mount it in water on a slip, with 
the under side uppermost, we can then examine it for the 




Fig. 304- 
Male prothallium of a fern (nip ho bolus), in form of an alga or protonema. Spermato- 
zoids escaping from antheridia. 

sexual organs, for these are borne in most cases on the under 
side. 

556. Antheridia. — If Ave search among the rhizoids wc see 
small rounded elevations as shown in fig. 297 or 305 scat- 




Fig. 305. 

Male prothallium of fern (niphobolus), showing opened and unopened antheridia ; sectim 
of unopened antheridium ; spermatozoids escaping ; spermatozgids which did not cscu^ 
from the antheridium. 



FERNS. 



267 




tered over this portion of the prothallium. These are the an- 
theridia. Ifthepro- 
thallia have not been 
watered for a day or 
so, we may have an 
opportunity of see- 
ing the spermato- 
zoids coming out of 
the antheridium, for 

when the prothallia Section of antheridia showing sperm cells, and spermato- 

are freshly placed in zoids in the one at the right - 

water the cells of the antheridium ab- 
sorb water. This presses on the con- 
tents of the antheridium and bursts the 
cap cell if the antheridium is ripe, and 
all the spermatozoids are shot out. 
We can see here that each one is 
shaped like a screw, with the coils at 

Fig. 307. l ' 

Different views of spermatozoids; first close. But aS the SpermatOZOid 
in a quiet condition; in motion ,. . .. 

(Adiantum concinnum). begins tO fflOVe thlS COll OpeilS SOffle- 

what and by the vibration of 
the long cilia which are on the 
smaller end it whirls away. In 
such preparations one may often 
see them spinning around for a 
long while, and it is only when 
they gradually come to rest 
that one can make out their 
form. 

557. Archegonia. — If we now 
examine closely on the thicker 
part of the under surface of the 
prothallium, just back of the 
"sinus," we may see 





Fig. 308. 



1 Archegonium of fern. Large cell in the 

longer venter is the egg, next is the ventral canal 

_ cell, and in the canal of the neck are two 

StOUt projections from the Surface nuclei of the canal cell. 

gf the prothallium. These are shown in fig. 297. They are 



268 



MORPHOLOGY. 



the archegonia. One of them in longisection is shown in fig. 
308. It is flask-shaped, and the broader portion is sunk in the 







Fig. 309. 
Mature and open archegonium of fern (Adiantum cuneatum) with spermatozoids making 
their way down through the slime to the egg. 

tissue of the prothallium. The egg is in the larger part. The 
spermatozoids when they are swimming 
around over the under surface of the pro- 
thallium come near the neck, and here they 
are caught in the viscid substance which 
has oozed out of the canal of the arche- 
gonium. From here they slowly swim 
down the canal, and finally one sinks into 
the egg, fuses with the nucleus of the latter, 
and the egg is then fertilized. It is now 
ready to grow and develop into the fern 
plant. This brings us back to the sporo- 

phyte, which begins with the fertilized egg. 




Fertilization in a fern 
' Marattia). s/>, spermato- 
zoid fusing with the nu- 
cleus of the egg. (After 

Campbell. 1 



Sporophyte. 

558. Embryo. — The egg first divides into two cells as shown in fig. 228, then 
into four. Now from each one of these quandrants of the embryo a definite 
part of the plant develops, from one the first leaf, from one the stem, from 
one the root, and from the other the organ which is called the foot, and which 



FERNS. 



269 



attaches the embryo to the prothallium, and transports nourishment for the 
embryo until it can become attached to the soil and lead an independent ex- 
istence. During this time the wall of the archegonium grows somewhat to 
accommodate the increase in size of the embryo, as shown in figs. 312, 313. 
But soon the wall of the archegonium is ruptured and the embryo emerges, 
the root attaches itself to the soil, and soon the prothallium dies. 

The embryo is first on the under side of the prothallium, and the first leaf 




Fig. 311- 
Two-celled embryo of Pteris serrulata. Remnant of archegonium neck below. 



and the stem curves upward between the lobes of the heart-shaped body, and 
then grows upright as shown in fig. 314. Usually only one embryo is formed 
on a single prothallium, but in one case I found a prothallium with two well- 
formed embryos, which are figured in 315. 

559. Comparison of ferns with liverworts and mosses. — In the ferns then 
we have reached a remarkable condition of things as compared with that 
which we found in the mosses and liverworts. In the mosses and liverworts 



270 



MORPHOLOGY. 



the sexual phase of the plant (gametophyte) was the prominent one, 
and consisted of either a th alius or a leafy axis, but in either case it bore the 
sexual organs and led an independent existence; that is it was capable of ob- 
taining its nourishment from the soil or water by means of organs of absorp- 
tion belonging to itself, and it also performed the office of photosynthesis. 

560. The spore -bearing phase (sporophyte) of the liverworts and mosses, 
on the other hand, is quite small as compared' with the sexual stage, and it is 




Fig. 312. 

Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium. ^9, 
stem ; L, first leaf or cotyledon ; R, root ; F, foot. 



completely dependent on the sexual stage for its nourishment, remaining at- 
tached permanently throughout all its development, by means of the organ 
called a foot, and it dies after the spores are mature. 

561. Now in the ferns we see several striking differences. In the first 
place, as we have already observed, the spore-bearing phase (sporophyte) of 



FERNS. 



2J1 



the plant is the prominent one, and that which characterizes the plant. It 
also leads an independent existence, and, with the exception of a few cases, 
does not die after the development of the spores, but lives from year to year 
and develops successive crops of spores. There is a distinct advance here in 
the size, complexity, and permanency of this phase of the plant. 

•562. On the other hand the sexual phase of the ferns (gametophyte), while 
it still is capable of leading an independent existence, is short dived (with very 
jCw exceptions). It is also much smaller than most of the liverworts and 




Embryo of fern (Adiantum concinnum) still surrounded by the archegonium, which has 
grown in size, forming the " calyptra." L, leaf ; S, stem ; R, root ; F, foot. 

mosses, especially as compared with the size of the spore-bearing phase. 
The gametophyte phase or stage of the plants, then, is decreasing in size and 
durance as the sporophyte stage is increasing. We shall be interested to see 
if this holds good of the fern allies, that is of the plants which belong to the 
same group as the ferns. And as we come later to take up the study of the 
higher plants we must bear in mind to carry on this comparison, and see if 
this progression on the one hand of the sporophyte continues, and if the 
retrogression of the gametophyte continues also. 



2J2 



MORPHOLOG V. 





Fig. 314. 
Young plant of Pteris serrulata still 
attached to prothallium. 



Fig- 31S. 
Two embryos from one prothallium of 
Adiantum cuneatum. 



CHAPTER XXVIII. 

DIMORPHISM OF FERNS. 

563. In comparing the different members of the leaf series 
there are often striking illustrations of the transition from one 
form to another, as we have noted in the case of the trillium 
flower. This occurs in many other flowers, and in some, as in 
the water lily, these transformations are always present, here 
showing a transition from the petals to the stamens. In the bud 
scales of many plants, as in the butternut, walnut, currant, etc., 
there are striking gradations between the form of the simple bud 
scales and the form of the leaf. Some of the most interesting of 
these transformations are found in the dimorphic ferns. 

564. Dimorphism in the leaves of ferns. — In the common 
polypody fern, the maidenhair, and in many other ferns, all the 
leaves are of the same form. That is, there is no difference be- 
tween the fertile leaf and the sterile leaf. On the other hand, in 
the case of the Christmas fern we have seen that the fertile 
leaves are slightly different from the sterile leaves, the former 
having shorter pinnae on the upper half of the leaf. The fertile 
pinnae are here the shorter ones, and perform but little of the 
function of carbon conversion. This function is chiefly per- 
formed by the sterile leaves and by the sterile portions of the 
fertile leaves. This is a short step toward the division of labor 
between the two kinds of leaves, one performing chiefly the labor 
of carbon conversion, the other chiefly the labor of bearing the 
fruit. 

565. The sensitive fern. — This division of labor is carried to 
an extreme extent in the case of some ferns. Some of our native 

273 



274 



MORPHOLOG Y. 



ferns are examples of this interesting relation between the leaves 
like the common sensitive fern (Onoclea sensibilis) and the 
ostrich fern (O. struthiopteris) and the cinnamon fern (Osmunda 
cinnamomea). The sensitive fern is here shown in fig. 316. 
The sterile leaves are large, broadly expanded, and pinnate, the 




Fig. 316. 
Sensitive fern ; normal condition of vegetative leaves and sporophylls. 

pinnae being quite large. The fertile leaves are shown also in 
the figure, and at first one would not take them for leaves at all. 
But if we examine them carefully we see that the general plan 
of the leaf is the same : the two rows of pinnae which are here 
much shorter than in the sterile leaf, and the pinnules, or smaller 



DIMORPHISM OF FERNS. 



*7$ 



divisions of the pinnae, are inrolled into little spherical masses 
which lie close on the side of the pinnae. If we unroll one of 
these pinnules we find that there are several fruit dots within 
protected by this roll. In fact when the spores are mature these 




Fig. 317. 

Sensitive fern ; one fertile leaf nearly changed to vegetative leaf. 

pinnules open somewhat, so that the spores may be dissemi- 
nated. 

There is very little green color in these fertile leaves, and 
what green surface there is is very small compared with that of 
the broad expanse of the sterile leaves. So here there is practi- 
cally a complete division of labor between these two kinds of 



s;6 



MORPHOLOGY. 



leaves, the general plan of which is the same, and we recognize 
each as being a leaf. 

566. Transformation of the fertile leaves of onoclea to 
sterile ones. — It is not a very rare thing to find plants of the 
sensitive fern which show intermediate conditions of the sterile 
and the fertile leaf. A number of years ago it was thought by 
some that this represented a different species, but now it is known 



V 




4& ■ 






1 /^*V 



Fig. 3i 8. 
Sensitive fern, showing one vegetative leaf and two sporophylls completely transformed. 



that these intermediate forms are partly transformed fertile leaves. 
It is a very easy matter in the case of the sensitive fern to pro- 
duce these transformations by experiment. If one in the spring, 
when the sterile leaves attain a height of 12 to 16 cm (8-10 
inches), cuts them away, and again when they have a second 
time reached the same height, some of the fruiting leaves which 
develop later will be transformed. A few years ago I cut off the 



DIMORPHISM OF FERNS. 



277 



sterile leaves from quite a large patch of the sensitive fern, once 
in May, and again in June. In July, when the fertile leaves 
were appearing above the ground, many of them were changed 
partly or completely into sterile leaves. In all some thirty plants 




Fig. 319. 
Normal and transformed sporophyll of sensitive fern. 

showed these transformations, so that every conceivable gradation 
was obtained between the two kinds of leaves. 

567. It is quite interesting to note the form of these changed 
leaves carefully, to see how this change has affected the pinnae 
and the sporangia. We note that the tip of the leaf as well as 
t\\e tips of all the pinnae are more expanded than the basal por- 



278 MORPHOL OGY. 

tions of the same. This is due to the fact that the tip of the 
leaf develops later than the basal portions. At the time the 
stimulus to the change in the development of the fertile leaves 
reached them they were partly formed, that is the basal parts of 
the fertile leaves were more or less developed and fixed and 
could not change. Those portions of the leaf, however, which 
were not yet completely formed, under this stimulus, or through 
correlation of growth, are incited to vegetative growth, and ex- 
pand more or less completely into vegetative leaves. 

568. The sporangia decrease as the fertile leaf expands. — 
If we now examine the sporangia on the successive pinnae of a 
partly transformed leaf we find that in case the lower pinnae are 
not changed at all, the sporangia are normal. But as we pass to 
the pinnae which show increasing changes, that is those which are 
more and more expanded, we see that the number of sporangia 
decrease, and many of them are sterile, that is they bear no 
spores. Farther up there are only rudiments of sporangia, until 
on the more expanded pinnae sporangia are no longer formed, 
but one may still see traces of the indusium. On some of the 
changed leaves the only evidences that the leaf began once to 
form a fertile leaf are the traces of these indusia. In some of 
these cases the transformed leaf was even larger than the sterile 
leaf. 

569. The ostrich fern. — Similar changes were also produced 
in the case of the ostrich fern, and in fig. 319 is shown at the 
left a normal fertile leaf, then one partly changed, and at the 
right one completely transformed. 

570. Dimorphism in tropical ferns. — Very interesting forms 
of dimorphism are seen in some of the tropical ferns. One of 
these is often seen growing in plant conservatories, and is known 
as the staghorn fern (Platy cerium alcicorne). This in nature 
grows attached to the trunks of quite large trees at considerable 
elevations on the tree, sometimes surrounding the tree with a 
massive growth. One kind of leaf, which may be either fertile 
or sterile, is narrow, and branched in a peculiar manner, so that 
it resembles somewhat the branching of the horn of a stag. 



DIMORPHISM OF FERNS. 



279 



Below these are other leaves which are different in form and 
sterile. These leaves are broad and hug closely around the roots 
and bases of the other leaves. Here they serve to catch and 




Fig. 320. 
Ostrich fern, showing one normal sporophyll, one partly transformed, and one completely 
transformed. 



retain moisture, and they also catch leaves and other vegetable 
matter which falls from the trees. In this position the leaves 
decay and then serve as food for the fern. 



CHAPTER XXIX. 



HORSETAILS. 



571. Among the relatives of the ferns are the 
horsetails, so called because of the supposed resem- 
blance of the branched stems of some of the species 
to a horse's tail, as one might infer from the plant 
shown in fig. 325. They do not bear the least re- 
semblance to the ferns which we have been study- 
ing. But then relationship in plants does not depend 
on mere resemblance of outward form, or of the promi- 
nent part of the plant. 

572. The field equisetum. Fertile shoots. — Fig. 
321 represents the common horsetail (Equisetum ar- 
vense). It grows in moist sandy or gravelly places, 
and the fruiting portion of the plant (for this species 
is dimorphic), that is the portion which bears the 
spores, appears above the ground early in the spring. 
It is one of the first things to peep out of the recently 
frozen ground. This fertile shoot of the plant does 
not form its growth this early in the spring. Its 
development takes place under the ground in the 
autumn, so that with the advent of spring it pushes 
up without delay. This shoot is from 10 to 20 
cm high, and at quite regular intervals there are 
slight enlargements, the nodes of the stem. The 
cylindrical portions between the nodes are the 
internodes. If we examine the region of the inter- ^^ % of 
nodes carefully we note that there are thin mem- EquiLulm *a?- f 
branous scales, more or less triangular in outline, and who5s Showl of 
connected at their bases into a ring around the stem. frSg*"^ 6 

280 




HORSETAILS. 28 1 

Curious as it may seem, these are the leaves of the horsetail. 
The stem, if we examine it farther, will be seen to possess numer- 
ous ridges which extend lengthwise and which alternate with 
furrows. Farther, the ridges of one node alternate with those 
of the internode both above and below. Likewise the leaves 
of one node alternate with those of the nodes both above and 
below. 

573. Sporangia. — The end of this fertile shoot we see pos- 
sesses a cylindrical to conic enlargement. This is the fertile 
spike, and we note that its surface is marked off 
into regular areas if the spores have not yet been 
disseminated. If we dissect off a few of these por- 
tions of the fertile spike, and examine one of them 
with a low magnifying power, it will appear like the 
fig. 322. We see here that the angular area is a 
Fig. 322. disk-shaped body, with a stalk attached to its inner 
phyUo?equ?se°u?n surface, and with several long sacs projecting from 
Sng e S pm-rn g ia °on its inner face parallel with the stalk and surrounding 
the same. These elongated sacs are the sporangia, 
and the disk which bears them, together with the stalk which 
attaches it to the stem axis, is the sporophyll, and thus belongs to 
the leaf series. These sporophylls are borne in close whorls on 
the axis. 

574. Spores. — When the spores are ripe the tissue of the 
sporangium becomes dry, and it cracks open and the spores fall 
out. If we look at fig. 323 we see that the spore is covered 
with a very singular coil which lies close to the wall. When the 
spore dries this uncoils and thus rolls the spore about. Merely 
breathing upon these spores is sufficient to make them perform 
very curious evolutions by the twisting of these four coils which 
are attached to one place of the wall. They are formed by the 
splitting up of an outer wall of the spore. 

575. Sterile shoot of the common horsetail. — When the 
spores are ripe they are soon scattered, and then the fertile 
shoot dies down*. Soon afterward, or even while some of the 
fertile shoots are still in good condition, sterile shoots of the 



282 



MORPHOLOGY. 



plant begin to appear above the ground. One of these is shown 
in fig. 325. This has a much more slender stem and is pro- 





Fig. 323. Fig. 324- 

Spore of equisetum Spore of equisetum with elaters un 

with elaters coiled up. coiled. 

vided with numerous branches. If we ex- 
amine the stem of this shoot, and of the 
branches, we see that the same kind of 
leaves are present and that the markings on 
the stem are similar. Since the leaves of 
the horsetail are membranous and not green, 
the stem is green in color, and this per- 
forms the function of photosynthesis. These 
green shoots live for a great part of 
the season, building up material which is 
carried down into the underground stems, 
where it goes to supply the forming fertile 
shoots in the fall. On digging up some of 
these plants we see that the underground 
stems are often of great extent, and that 
both fertile and sterile shoots are attached 
to one and the same. 

576. The scouring rush, or shave grass. 
— Another common species of horsetail in 
the Northern States grows on wet banks, 
or in sandy soil which contains moisture 
along railroad embankments. It is 
the scouring rush (E. hyemale), so 
called because it was once used for 
polishing purposes. This plant like 
all the species of the horsetails has JKJ^gg. ° f horseUil (E ^ 




„Fig. 325. 



HORSE TA ILS. 283 

underground stems. But unlike the common horsetail, there is 
but one kind of aerial shoot, which is green in color and fertile. 
The shoots range as high as one meter or more, and are quite 
stout. The new shoots which come up for the year are un- 
branched, and bear the fertile spike at the apex. When the 
spores are ripe the apex of the shoot dies, and the next season 
small branches may form from a number of the nodes. 

577. Gametophyte of equisetum. — The spores of equisetum have chloro- 
phyll when they are mature, and they are capable of germinating as soon as 
mature. The spores are all of the same kind as regards size, just as we 
found in the case of the ferns. But they develop prothallia of different 
sizes, according to the amount of nutriment which they obtain. Those 
which obtain but little nutriment are smaller and develop only antheridia, 
while those which obtain more nutriment become larger, more or less 
branched, and develop archegonia. This character of an independent pro- 
thallium (gametophyte) with the characteristic sexual organs, and the also 
independent sporophyte, with spores, shows the relationship of the horsetails 
with the ferns. We thus see that these characters of the reproductive 
organs, and the phases and fruiting of the plant, are more essential in deter- 
mining relationships of plants than the mere outward appearances. 



CHAPTER XXX. 



CLUB MOSSES. 



578. What are called the "club mosses" make up another 
group of interesting plants which rank as allies of the ferns. 
They are not of course true mosses, but the general habit of 
some of the smaller species, and especially the 
form and size of the leaves, suggest a resem- 
blance to the larger of the moss plants. 

579. The clavate lycopodium. — Here is one 
of the club mosses (fig. 326) which has a wide 
distribution and which is well entitled to hold 
the name of club because of the form of the up- 
right club-shaped branches. As will be seen 
from the illustration, it has a prostrate stem. 
This stem runs for considerable distances on 
the surface of the ground, often partly buried in 
ihe leaves, and sometimes even buried beneath 
the soil. The leaves are quite small, are flat- 
tened-awl-shaped, and stand thickly over the 
stem, arranged in a spiral manner, which is the 
usual arrangement of the leaves of the club 
mosses. Here and there are upright branches 
which are forked several times. The end of 
one or more of these branches becomes pro- 
duced into a slender upright stem which is T x f." 32 ' , 

1 ° Lycopodium clava- 

nearly leafless, the leaves being reduced to ^-n^rSce^^riTt 
mere scales. The end of this leafless branch s P or °P h .yii with open 

sporangium ; single 

then terminates in one or several cylindrical s P° renear it- 
heads which form the club. 




CLUB MOSSES. 



285 



580. Fruiting spike of Lycopodium clavatum. — This club is 
the fruiting spike or head (sometimes termed a.s/ro5ilus). Here 
the leaves are larger again and broader, but still not so large as 
the leaves on the creeping shoots, and they are paler. If we bend 
down some of the leaves, or tear off a few, we see that in the 
axil of the leaf, where it joins the stem, there is a somewhat 
rounded, kidney -shaped body. This is the spore-case or spo- 
rangium, as we can see by an examination of its contents. There 
is but a single spore-case for each of the fertile leaves (sporophyll). 
When it is mature, it opens by a crosswise slit as seen in fig. 326. 
When we consider the number of spore-cases in one of these club- 
shaped fruit bodies we see that the number of spores developed 
in a large plant is immense. In mass the spores make a very fine, 
soft powder, which is used for some 
kinds of pyrotechnic material, and for 
various toilet purposes. 

581. Lycopodium lucidulum. — Another com- 
mon species is figured at 327. This is Lycopo- 
dium lucidulum. The habit of the plant is quite 
different. It grows in damp ravines, woods, and 
moors. The older parts of the stem are prostrate, 
while the branches are more or less ascending. 
It branches in a forked manner. The leaves are 
larger than in the former species, and they are 
all of the same size, there being no appreciable 
difference between the sterile and 
fertile ones. The characteristic 
club is not present here, but the 
spore-cases occupy certain regions of 
the stem, as shown at 327. In a 
single season one region of the stem 
may bear spore-cases, and then a 
sterile portion of the same stem is 

T j' 1 -j 1 i* iu-1 • 1 f developed, which later bears another 

Lycopodium lucidulum, bulbils in axils or r 

leaves near the top, sporangia in axils of leaves series of spore-cases higher up. 

below them. At right is a bulbil enlarged. -.".... 

582. Bulbils on Lycopodium 
lucidulum.— There is one curious way in which this club moss multiplies. 
One may see frequently among the upper leaves small wedge-shaped or heart- 
shaped green bodies but little larger than the ordinary leaves. These are little 




286 



MORPHOLOGY. 



buds which contain rudimentary shoot and root and several thick green leaves. 
When they fall to the ground they grow into new lycopodium plants, just as 
the bulbils of cystopteris do which were described in the chapter on ferns. 

583. Note. — The prothallia of the species of lycopodium which have been 
studied are singular objects. In L. cernuum a cylindrical body sunk in the 
earth is formed, and from the upper surface there are green lobes. In L. 
phlegmaria and some others slender branched, colorless bodies are formed 
which according to Treub grow as a saphrophyte in decayed bark of trees. 
Many of the prothallia examined have a fungus growing in their tissue which 
is supposed to play some part in the nutrition of the prothallium. 



The little club mosses (selaginella). 

584. Closely related to the club mosses are the selaginellas. 
These plants resemble closely the general habit of the club mosses, 
but are generally smaller and the leaves more delicate. Some 
species are grown in conservatories for ornament, the leaves of 




Fig. 328. Fig. 329. 

Selaginella with Fruiting spike 

three fruiting spikes, showing large and 

(Selaginella apus.) small sporangia. 



Fig. 330. Fig. 331. 

Large spo- Small spo- 
rangium, rangium. 



such usually having a beautiful metallic lustre. The leaves of some 
are arranged as in lycopodium, but many species have the leaves 
in four to six rows. Fig. 328 represents a part of a selaginella 
plant (S. apus). The fruiting spike possesses similar leaves, but 
they are shorter, and their arrangement gives to the spike a four- 
sided appearance. 



1 1 1 n t ww 



LITTLE CLUB MOSSES. 



2S7 



585. Sporangia. — On examining the fruiting spike, we find 
as in lycopodium that there is but a single sporangium in the 
axil of a fertile leaf. But we see that they are of two different 
kinds, small ones in the axils of the upper leaves, and large ones 
in the axils of a few of the lower leaves of the spike. The micro- 
spores are borne in the smaller spore-cases and the macrospores 
in the larger ones. Figures 329-331 give the details. There 
are many microspores in a single small spore-case, but 3-4 ma- 
crospores in a large spore-case. 

586. Male prothallia. — The prothallia of selaginella are much 
reduced structures. The microspores when mature are already 
divided into two cells. When they grow into the mature pro- 
thallium a few more cells are formed, and some of the inner ones 
form the spermatozoids, as seen in fig. 332. Here we see that 




Fig. 332. 
Details of microspore and male prothallium of selaginella ; ist, microspore ; 2d, wall re- 
moved to show small prothallial cell below ; 3d, mature male prothallium still within the 
wall ; 4th, small cell below is the prothallial cell, the remainder is antheridium with wall and 
four sperm cells within ; 5th spermatozoid. After Beiiaieff and Pfeffer. 

the antheridium itself is larger than the prothallia. Only an- 
theridia are developed on the prothallia formed from the 
microspores, and for this reason the prothallia are called male 
prothallia. In fact a male prothallium of selaginella is nearly 
all antheridium, so reduced has the gametophyte become here. 

587. Female prothallia. —The female prothallia are devel- 
oped from the macrospores. The macrospores when mature have 
a rough, thick, hard wall. The female prothallium begins to 
develop inside of the macrospore before it leaves the sporangium. 
The protoplasm is richer near the wall of the spore and at the 



288 



MORPHOLOGY. 



upper end. Here the nucleus divides a great many times, and 
finally cell walls are formed, so that a tissue of considerable ex- 
tent is formed inside the wall of the spore, which is very 
different from what takes place in the ferns we have 
studied. As the prothallium matures the spore is cracked 
at the point where the three angles meet, as shown in 
fig. 334. The archegonia are developed in this exposed 
surface, and several can be seen in the illustration. 

588. Embyro. — After fertilization the egg divides in such a way 
that a long cell called a suspensor is cut off from the upper side, 






Fig- 333- Fig- 334- 

Section of mature macrospore Mature female prothallium of Fig. 335* 

of selaginella, showing female selaginella, just bursting open Seedling of sela- 

prothallium and archegonia. the wall of macrospore, exposing ginella still attached 
After Pfeffer. archegonia. After Pfeffer. to the macrospore. 

After Campbell. 

which elongates and pushes the developing embyro down into the center of 
the spore, or what is now the female prothallium. Here it derives nourish- 
ment from the tissues of the prothallium, and eventually the root and stem 
emerge, while a process called the " foot " is still attached to the prothallium. 
When the root takes hold on the soil the embyro becomes free. 



■iiiiiiuif 




Fig. 336. 
Isoetes, mature plant, sporophyte stage 



which is triangular. 



CHAPTER XXXI. 

QUILLWORTS (ISOETES). 

589. The quill worts, as they 
are popularly called, are very 
curious plants. They grow in 
wet marshy places. They receive 
their name from the supposed 
resemblance of the leaf to a quill. 
Fig. 336 represents one of these 
quillworts (Isoetes engelmannii). 
The leaves are the prominent 
part of the plant, and they are 
about all that can be seen except 
the roots, without removing the 
leaves. Each leaf, it will be 
seen, is long and needle-like, ex- 
cept the basal part, which is 
expanded, not very unlike, in out- 
line, a scale of an onion. These 
expanded basal portions of the 
leaves closely overlap each other, 
and the very short stem is com- 
pletely covered at all times. Fig. 
338 is from a longitudinal sec- 
tion of a quillwort. It shows 
the form of the leaves from this 
view (side view), and also the 
general outline of the short stem, 

The stem is therefore a very short object. 

289 



290 



MORPHOLOGY. 



590. Sporangia of isoetes. — If we pull off some of the 
leaves of the plant we see that they are somewhat spoon-shaped 
as in fig. 337. In the inner surface of the expanded base we 
note a circular depression which seems to be of a different text- 




Fig- 337- 
Base of leaf of isoetes, 
showing sporangium with 
macrospores. (Isoetes en- 
gelmannii.) 




Fig. 338. 
Section of plant of Isoetes engelmanii, showing cup- 
shaped stem, and longitudinal sections of the sporan- 
gia in the thickened bases of the leaves. 



ure from the other portions of the leaf. This is a sporangium. 
Beside the spores on the inside of the sporangium, there are 
strands of sterile tissue which extend across the cavity. This is 
peculiar to isoetes of all the members of the class of plants to 
which the ferns belong, but it will be remembered that sterile 
strands of tissue are found in some of the liverworts in the form 
of elaters. 

591. The spores of isoetes are of two kinds, small ones 
(microspores) and large ones (macrospores), so that in this 
respect it agrees with selaginella, though it is so very different in 
other respects. When one kind of spore is borne in a sporan- 



QUILLWORTS. 29 1 

gium usually all in that sporangium are of the same kind, so that 
certain sporangia bear microspores, and others bear macrospores. 
But it is not uncommon to find both kinds in the same sporan- 
gium. When a sporangium bears only microspores the number 
is much greater than when one bears only macrospores. 

592. If we examine some of the microspores of isoetes we see that they are 
shaped like the quarters of an apple, that is they are of the bilateral type as 
seen in some of the ferns (asplenium). 

593. Male prothallia. — In isoetes, as in selaginella, the microspores de- 
velop only male prothallia, and these are very rudimentary, one division of 
the spore having taken place before the spore is mature, just as in selagi- 
nella. 

594. Female prothallia. — These are developed from the macrospores. The 
latter are of the tetrahedral type. The development of the female prothal- 
lium takes place in much the same way as in selaginella, the entire prothal- 
lium being enclosed in the macrospore, though the cell divisions take place 
after it has left the sporangium. When the archegonia begin to develop 
the macrospore cracks at the three angles and the surface bearing the arche- 
gonia projects slightly as in selaginella. Absorbing organs in the form of 
rhizoids are very rarely formed. 

595. Embryo. — The embryo lies well immersed in the tissue of the pro- 
thallium, though there is no suspensor developed as in selaginella. 



CHAPTER XXXII. 

COMPARISON OF FERNS AND THEIR RELATIVES. 

596. Comparison of selaginella and isoetes with the ferns. — On compar- 
ing selaginella and isoetes with the ferns, we see that the sporophyte is, as 
in the ferns, the prominent part of the plant. It possesses root, stem, and 
leaves. While these plants are not so large in size as some of the ferns, 
still we see that there has been a great advance in the sporophyte of selagi- 
nella and isoetes upon what exists in the ferns. There is a division of labor 
between the sporophylls, in which some of them bear microsporangia with 
microspores, and some bear macrosporangia with only macrospores. In the 
ferns and horsetails there is only one kind of sporophyll, sporangium, and 
spore in a species. By this division of labor, or differentiation, between the 
sporophylls, one kind of spore, the microspore, is compelled to form a male 
prothallium, while the other kind of spore, the macrospore, is compelled to 
form a female prothallium. This represents a progression of the sporophyte 
of a very important nature. 

597. On comparing the gametophyte of selaginella and isoetes with that 
of the ferns, we see that there has been a still farther retrogression in size 
from that which we found in the independent and large gametophyte of the 
liverworts and mosses. In the ferns, while it is reduced, it still forms 
rhizoids, and leads an independent life, absorbing its own nutrient materials, 
and assimilating carbon. In selaginella and isoetes the gametophyte does 
not escape from the spore, nor does it form absorbing organs, nor develop 
assimilative tissue. The reduced prothallium develops at the expense of 
food stored by the sporophyte while the spore is developing. Thus, while 
the gametophyte is separate from the sporophyte in selaginella and isoetes, 
it is really dependent on it for support or nourishment. 

598. The important general characters possessed by the ferns and their 
so-called allies, as we have found, are as follows: The spore-bearing part, 
which is the fern plant, leads an independent existence from the prothallium, 
and forms root, stem, and leaves. The spores are borne in sporangia on 
the leaves. The prothallium also leads an independent existence, though in 
isoetes and selaginella it has become almost entirely dependent on the sporo- 

292 



COMPARISON OF FERNS. 293 

phyte. The prothallium bears also well-developed antheridia and arche- 
gonia. The root, stem, and leaves of the sporophyte possess vascular 
tissue. All the ferns and their allies agree in the possession of these char- 
acters. The mosses and liverworts have well-developed antheridia and 
archegonia, and the higher plants have vascular tissue. But no plant of 
either of these groups possesses the combined characters which we find in 
the ferns and their relatives. The latter are, therefore, the fern-like plants, 
or pteridophyla. The living forms of the pteridophyta are classified as fol- 
lows into families or orders. (See page 295.) 



2 9 4 



MORPHOLOGY. 



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FERNS: CLASSIFICATION. 295 



Classification of the Pteridophytes. 

Of the living pteridophytes four classes may be recognized. 
CLASS FILICINE.E.* 

This class includes the ferns. Four orders may be recognized. 

600. Order Ophioglossales. (One Family, Ophioglossaceae). — This order 
includes the grapeferns (Botrychium), so called because of the large 
botryoid cluster of sporangia, resembling roughly a cluster of grapes; and 
the adder-tongue (Ophioglossum), the sporangia being embedded in a long 
tongue-like outgrowth from the green leaf. Botrychium and Ophioglos- 
sum are widely distributed. The roots are fleshy, nearly destitute of root 
hairs, and contain an endophytic fungus, so that the roots are mycorhiza. 
The gametophyte is subterranean, and devoid of chlorophyll. In Botry- 
chium virginianum, an endophytic fungus has been found in the prothal- 
lium. Another genus (Helminthostachys) with one species is limited to 
the East Indies. 

601. Order Marattiales (One Family, Marattiaceae). — These are trop- 
ical ferns, with only four or five living genera (Marattia, Danaea, etc.). 
They resemble the typical ferns, but the sporangia are usually united, sev- 
eral forming a compound sporangium, or synangium. 

The Ophioglossales and Marattiales are known as eusporangiate ferns, 
while the following order includes the leptosporangiate ferns. 

602. Order Filicales. — This order includes the typical ferns. Eight 
families are recognized. 

Family Osmundacea. — Three genera are known in this family. Os- 
munda has a number of species, three of which are found in the Eastern 
United States; the cinnamon-fern (O. cinnamomea), the royal fern (O. 
regalis), and Clayton's fern (O. claytoniana). Xo species of this family 
are found on the Pacific coast. 

Family Glciclieniacac. — These ferns are found chiefly in the tropics, and 
in the mountain regions of the temperate zones of South America. There 
are two genera, Gleichenia containing all but one of the known species. 

Family Matoniacccr— One genus, Matonia, in the Malayan region. 

Family Schizoeacece. — These are chiefly tropical, but two species are 
found in eastern North America, Schizaea pusilla and Lygodium palma- 
tum, the latter a climbing fern. 

Family Hymcnopliyllacca'. — These are known as the filmy ferns because 
of their thin, delicate leaves. They grow only in damp or wet regions, 
mostly in the tropics, but a few species occur in the southern United States. 

Family Cyatheacecc. — These are known as the tree-ferns, because, of the 



::: As class Filicales in Engler and Prantl. 



296 MORPHOLOG Y. 

large size which many of them attain. They occur chiefly in tropical moun- 
tainous regions, many of them palm-like and imposing because of the large 
trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are some of 
the most conspicuous genera. 

Family Parkeriacece. — There is a single species in this family (Cera- 
topteris thalictroides), abundant in the tropics and extending into Florida. 
It is aquatic. 

Family Polypodiacece. — This family includes the larger number of living 
ferns and many genera and species are found in North America. Exam- 
ples, Polypodium, Pteridium (=Pteris), Adiantum, etc. 

603. Order Hydropterales (or Salviniales). — The members of this order 
are peculiar, aquatic ferns, some floating on the water (Azolla, Salvinia), 
while others are anchored to the soil by roots (Marsilia, Pilularia). They 
are known as water ferns. The sporangia are of two kinds, one containing 
large spores (macrospores) and the other small spores (microspores). They 
are therefore heterosporous ferns. 

Family Salviniacea. — There are two genera, Salvinia and Azolla. 
Family Marsiliacea. — Two genera, Marsilia and Pilularia. In this family 
the sporangia are enclosed in a sporocarp, which forms a pod-like structure. 
CLASS EQUISETINE.2E.* 

604. Order Equisetales. — The single order contains a single family, 
Equisetaceae, among the living forms, and but a single genus, Equisetum. 
There are about twenty-four species, with fourteen in the United States (see 
Chapter XXIX). 

CLASS LYCOPODIINE^.f 

605. Order Lycopodiales. — The first two families of this order include 
the homosporous Lycopodiineae, while the Selaginellaceae are heterosporous. 

Family Lycopodiacece. — There are two genera. Lycopodium (club 
moss) includes many species, most of them tropical, but a number in tem- 
perate and subarctic regions. The gametophyte of many species is tuber- 
ous, lacks chlorophyll, and in some there lives an endophytic fungus. Phyl- 
loglossum with one species is found in Australia. 

Family Psilotacece. — There are two genera. Psilotum chiefly in the 
tropics has one species (P. triquetrum) in the region of Florida. 

Family Selaginellacece. — These include the little club mosses, with one 
genus, Selaginella (see Chapter XXX). 

CLASS ISOETINEJE. 

606. Order Isoetales, with one family Isoetaceae and one genus Isoetes 
(see Chapter XXXI). There are about fifty species, with about sixteen in 
the United States. 



* As class Equisetales in Engler and Prantl. 
I As class Lycopodiales in Engler and Prantl. 



CHAPTER XXXIII. 

GYM NOSPERMS. 

The white pine. 

607. General aspect of the white pine. — The white pine 
(Pinus strobus) is found in the Eastern United States. In 
favorable situations in the forest it reaches a height of about 50 
meters (about 160 feet), and the trunk a diameter of over 1 
meter. In well-formed trees the trunk is straight and towering; 
the branches where the sunlight has access and the trees are not 
crowded, or are young, reaching out in graceful arms, form a 
pyramidal outline to the tree. In old and dense forests the lower 
branches, because of lack of sunlight, have died away, leaving 
tall, bare trunks for a considerable height. 

608. The long shoots of the pine. — The branches are of two kinds. Those 
which we readily recognize are the long branches, so called because the 
growth in length each year is considerable. The terminal bud of the long 
branches, as well as of the main stem, continues each year the growth of the 
main branch or shoot; while the lateral long branches arise each year from 
buds which are crowded close together around the base of the terminal bud. 
The lateral long branches of each year thus appear to be in a whorl. The 
distance between each false whorl of branches, then, represents one year's 
growth in length of the main stem or long branch. 

609. The dwarf shoots of the pine. — The dwarf branches are all lateral 
on the long branches, or shoots. They are scattered over the year's growth, 
and each bears a cluster of five long, needle-shaped, green leaves, which 
remain on the tree for several years. At the base of the green leaves are 
a number of chaff-like scales, the previous bud scales. While the dwarf 
branches thus bear green leaves, and scales, the long branches bear only 
thin scale-like leaves which are not green, 

297 



298 



MORPHOLOGY. 



610. Spore-bearing leaves of the pine. — The two kinds of 
spore -bearing leaves of the pine, and their close relatives, are 
so different from anything which we have yet studied, and are 
so unlike the green leaves of the pine, that we would scarcely 
recognize them as belonging to this category. Indeed there is 
great uncertainty regarding their origin. 

611. Male cones, or male flowers. — The male cones are borne 
in clusters as shown in fig. 330. Each compact, nearly cylindri- 




Fig. 339- 
Spray of white pine showing cluster of male cones just before the scattering of the pollen. 



cal, or conical mass is termed a cone, or flower, and each arises 
in place of a long lateral branch. One of these cones is shown 



GYMNOSPERMS: WHITE PINE. 



299 



considerably enlarged in fig. 340. The central axis of each 
cone is a lateral branch, and belongs to the stem series. The 
stem axis of the cone can be seen in fig. 341. It is completely 
covered by stout, thick, scale-like outgrowths. These scales 
are obovate in outline, and at the inner angle of the upper end 




Fig. 340. Fig. 341- Fig. 342. 

Staminate cone of white Section of staminate Two sporo- 

pine, with bud scales re- cone, showing sporangia, phylls removed, 
moved on one side. showing open- 

ing of sporangia. 

there are several rough, short spines. They are attached by 
their inner lower angle, which forms a short stalk or petiole, 
and continues through the inner face of the scale as a ''mid- 
rib." What corresponds to the lamina of the scale-like leaf 
bulges out on each side below and makes the bulk of the scale. 
These prominences on the under side are the sporangia (micro- 
sporangia). There are thus two sporangia on a sporophyll 
(microsporophyll). When the spores (microspores), which 
here are usually called pollen grains, are mature each sporangium, 

or anther locule, splits down the middle as 

shown in fig. 342, and the spores are set free. 
612. Microspores of the pine, or pollen 

grains. — A mature pollen grain of the pine is 
of shown in fig. 343. It is a queer-looking object, 

possessing on two sides an air sac, formed by the 
upheaval of the outer coat of the spore at these two points. 




Fig. 343- 
Pollen grain 
white pine. 



3oo 



MORPHOLOGY. 



When the pollen is mature, the moisture dries out of the scale 
(or stamen, as it is often called here) while 
it ripens. When a limb, bearing a cluster 
of male cones, is jarred by the hand, or by 
currents of air, the split suddenly opens, and 
a cloud of pollen bursts out from the numer- 
ous anther locules. The pollen is 
thus borne on the wind and some of 

it falls on the 

female flowers. 





Fig. 344- 
White pine, branch with cluster of 
mature cones shedding the seed. A 
few young cones four months old 
are shown on branch at the left. 
Drawn from photograph. 

613. Form of the ma- 
ture female cone. — A 

cluster of the white- 
pine cones is shown in 
fig. 344. These are 
mature, and the scales 
have spread as they do when mature and becoming dry, in 
order that the seeds may be set at liberty. The general out- 



fig. 345- 
Mature cone of white pine 
at time of scattering of the 
seed, nearly natural size. 






GYMNOSPERMS: WHITE PINE. 



301 



line of the cone is lanceolate, or long oval, and somewhat 
curved. It measures about \o-\^cm long. If we remove one 




Fig. 346. Fig. 347- Fig. 348. Fig. 349- Fig. 350. 

Sterile scale. Scale with Seeds have Back of scale Winged 
Seeds undevel- well- developed split off from with small cover seed free from 
oped. seeds. scale. scale. scale. 

Figs. 346-350. — White pine showing details of mature scales and seed. 

of the scales, just as they are beginning to spread, or before the 
seeds have scattered, we shall find the seeds at- 
tached to the upper surface at the lower end. 
There are two seeds on each scale, one at each 
lower angle. They are ovate in outline, and 
shaped somewhat like a biconvex lens. At this 
time the seeds easily fall away, and may be 
freed by jarring the cone. As the seed is 
detached from the scale a strip of tissue from 
the latter is peeled off. This forms a " wing " 
for the seed. It is attached to one end and is 
shaped something like a knife blade. On the 
back of the scale is a small appendage known 
as the cover scale. 

614. Formation of the female pine cone. — The female 

flowers begin their development rather late in the spring 

of the year. They are formed from terminal buds of 

the higher branches of the tree. In this way the cone 

may terminate the main shoot of a branch, or of the 

Fig- 35i. lateral shoots in a whorl. Aftergrowth has proceeded 

Female cones of the for some time in the spring, the terminal portion begins 
pine at time of pollina- , r _ , 

tion, about natural size, to assume the appearance of a young female cone or 




302 



MORPHOLOGY. 



flower. These young female cones, at about the time that the pollen is 
escaping from the anthers, are long ovate, measuring about 6-iomm long. 
They stand upright as shown in fig. 351. 



615. 

one of 



m 



Form of a " scale " of the female flower. — If we remove 
the scales from the cone at this stage we can better study 
it in detail. It is flattened, and oval in 
outline, with a stout " rib," if it may be so 
called, running through the middle line and 
terminating in a point. The scale is in 
two parts as shown in fig. 354, which is a 
view of the under side. The small " out- 
growth ' ' which appears as an appendage is 
the cover scale, for while it is smaller in the 
pine than the other portion, in some of 
the relatives of the pine it is larger than its 
mate, and being on the outside, covers it. 
(The inner scale is sometimes called the ovu- 
liferous scale, because it bears the ovules. ) 

616. Ovules, or macrosporangia, of the 
pine. — At each of the lower angles of the 





Fig. 352. Fig. 353- Fig.354^ 

Section of female cone Scale of white pine with the Scale of white pine seen 

of white pine, showing two ovules at base of ovulif- from the outside, showing the 

young ovules (macrospo- erous scale. cover scale, 
rangia) at base of the ovu- 
lif erous scales. 

scale is a curious oval body with two curved, forceps-like pro- 
cesses at the lower and smaller end. These are the macro- 
sporangia, or, as they are called in the higher plants, the ovules. 
These ovules, as we see, are in the positions of the seeds on the 



GYMNOSPERMS: WHITE PINE. 



303 



mature cones. In fact the wall of the ovule forms the outer coat 
of the seed, as we will later see. 

617. Pollination. — At the time when the pollen is mature the 
female cones are still erect on the branches, and the scales, which 
during the earlier stages of growth were closely pressed against 
one another around the axis, are now 
spread apart. As the clouds of pollen 
burst from the clusters of the male cones, 
some of it is wafted by the wind to the 
female cones. It is here caught in the 
open scales, and rolls down to their bases, 
where some of it falls between these 
forceps-like processes at the 
lower end of the ovule. At 




Fig. 355. 
Branch of white pine showing young female cones at time of pollination on the ends of 
the branches, and one-year-old cones below, near the time of fertilization. 

this time the ovule has exuded a drop of a sticky fluid in this 
depression between the curved processes at its lower end. The 
pollen sticks to this, and later, as this viscid substance dries up, 
it pulls the pollen close up in the depression against the lower 



304 



M0RPH0L0G V. 



end of the ovule. This depression is thus known as the pollen 

chamber. 

618. Now the open scales on the young female cone close up 

again so tightly that water from rains is excluded. What is also 
very curious, the cones, which up to this 
time have been standing erect, so that 
the open scale could catch the pollen, 
now turn so that they hang downward. 
This more certainly excludes the rains, 
since the overlapping of the scales forms 
a shingled surface. Quantities of resin 
are also formed in the scales, which 
exudes and makes the cone practically 
impervious to water. 

619. The female cone now slowly 
grows during the summer and autumn, 
increasing but little in size during this 
time. During the winter it rests, that 




Pig- 35 6. 
Macrosporangium of pine 
(ovule), int, integument; n, 

^"JhSbSTTj&fi is > ceases t0 § row - With the comin g of 

fjongy tfssuT le (Sr e 'r f£- spring, growth commences again and 
guson ' ) at an accelerated rate. The increase in 

size is more rapid. The cone reaches maturity in September. 
We thus see that nearly eighteen months elapse from the begin- 
ning of the female flower to the maturity of the cone, and about 
fifteen months from the time that pollination takes place. 

620. Female prothallium of the pine. — To study this we must make care- 
ful longitudinal sections through the ovule (better made with the aid of a 
microtome). Such a section is shown in fig. 358. The outer layer of tis- 
sue, which at the upper end (point where the scale is attached to the axis of 
the cone) stands free, is the ovular coat, or integument. Within this integu- 
ment, near the upper end, there is a cone-shaped mass of tissue. This 
mass of tissue is the nucellus, or the macrosporangium proper. In the 
lower part of the nucellus in fig. 356 can be seen a rounded mass of "spongy 
tissue " (spt), which is a special nourishing tissue of the nucellus, or spo- 
rangium, around the macrospore. Within this can be seen an axile row 
of three cells (an : m). The lowest one, which is larger than the other 
two, is the macrospore. Sometimes there are four of these cells in the axile 
row. This axile row of three or four cells is formed by the two successive 



GYMNOSPERMS: WHITE PINE. 



305 




***« 



divisions of a mother cell in the nucellus. So it would appear that these 

three or four cells are all 

spores. 

Only one of them, however, 
the lower one, develops; the 
others are disorganized and 
disappear. The nucleus of 
the macrospore now divides 
several times to form several 
free nuclei in the now enlarg- 
ing cavity, much as the nu- 
cleus of the macrospore in Fig. 357- 

Selaginella and Isoetes divides . Pollen grains of pine. One of them germinat- 
6 ing. p l and p 2 , the two disintegrated prothalhal 

within the spore. The de- cells, = sterile part of male gametophyte; a.c, 
, , - , , , central cell of antheridium; v.n., vegetative nu- 

velopment thus far takes place cleus or tube nuc i eus G f the single-wall cell of 
during the first summer, and antheridium ; s.g. , starch grains. (After Ferguson.) 
now with the approach of winter the very young female prothallium goes 

into rest about the stage shown in 
fig. 358. The conical portion of 
the nucellus which lies above is the 
nucellar cap. 

621. Male prothallia. — By the 
time the pollen is mature the male 
prothallium is already partly 
formed. In fig. 343 we can see 
two well-formed cells. Two other 
cells are formed earlier, but they 
become so flattened that it is diffi- 
cult to make them out when the 
pollen grain is mature. These are 
shown in fig. 357, p l and p 2 , and 
they are the only sterile cells of the 
male prothallium in the pines. The 
large cell is the antheridium wall, 
its nucleus v.n. in fig. 357. The 
smaller cell, a.c, is the central cell 
of the antheridium. During the 
summer and autumn the male 
prothallium makes some farther 
growth, but this is slow. The 
Fig 358 . larger cell, called the vegetative 

Section of ovule of white pine, int, in- ce ll or tube cell, which is in reality 
tegument, pc, pollen chamber; pt, pollen a.„.j,«„„, ol«„ 

tube; n, nucleus; m, macrospore cavity. the wall of the antheridium, elon- 




306 



MORPHOLOGY. 



gates by the formation of a tube, forming a sac, known as the pollen tube. 
It is either simple or branched. It grows down into the tissue of the nu- 
cellus, and at a stage represented in fig. 358, winter overtakes it and it 
rests. At this time the central cell has divided into two cells, and the 
vegetative nucleus is in the pollen tube. 

622. The endosperm. — In the following spring growth of all these parts 




Fig. 359- 
Section of nucellus and endosperm of white pine. The inner layer of cells of 
the integument shown just outside of nucellus; arch, archegonium; en, egg nu- 
cleus. In the nucellar cap are shown three pollen tubes, vn, vegetative nucleus 
or tube nucleus; stc, stalk cell; spn, sperm nuclei, the larger one in advance is 
the one which unites with the egg nucleus. The archegonia are in the endosperm 
or female gametophyte. (After Ferguson.) 



continues. The nuclei in the macrospore divide to form more, and event- 
ually cell walls are formed between them making a distinct tissue, known 



GYMNOSPERMS: WHITE PINE. 



307 



as the endosperm. This endosperm continues to grow until a large part of 
the nucellus is consumed for food. 

623. Female prothallium and archegonia. — The endosperm is the female 
prothallium. This is very evident from the fact that severa* archegonia 
are developed in it usually on the side toward the pollen chamber. The 
archegonia are sexual organs, and since the sexual organs are developed on 
the gametophyte, therefore, the endosperm is the female gametophyte, or 
prothallium. In fig. 359 are represented two archegonia in the endosperm 
and the pollen tubes are growing down through the nucellus. The arche- 
gonia are quite large, the wall is a sheath or jacket of cells which encloses 
the very large egg which has a large nucleus in the center. 

624. Pollen tube and sperm cells. — While the endosperm (female pro- 
thallium) and archegonia are developing the pollen tube continues its 
growth down through the nucellar cap, as shown in fig. 359. At the same 
time the two cells which were formed in 
the pollen grain (antheridium) from the 
central cell move down into the tube. One 
of these is the " generative" cell, or "body" 
cell, and the other is called the stalk cell, 
though it is more properly a sterile half of 
the central cell. The nucleus of the gener- 
ative cell, about the time the archegonium 
is mature, divides to form two nuclei, 
which are the sperm nuclei, and the one 
in advance is the larger, though it is much 
smaller than the egg nucleus. 

625. Fertilization. — Very soon after the 
archegonia are mature (early in June in the 
northern United States) the pollen tube 
grows through into the archegonium and 
empties the two sperm nuclei, the vegetative 
nucleus and the stalk cell, into the proto- 
plasm of the large egg. The larger of the 
two sperm nuclei at once comes in contact 
with the very large egg nucleus and sinks 
down into a depression of the same, as 
shown in fig. 361. These two nuclei, in the 
pines, do not fuse into a resting nucleus, but 




Fig. 360. 
Last division of the egg in the 



at once organize the nuclear figure for the whit ? pi "f cutting off the ventral 

canal cell at the apex of the 



first division of the embryo. 
are thus formed, and these d 
four nuclei which sink to the bottom of the archegonium and there organ- 



Two nuclei archegonium. End, endosperm 
are thus formed, and these divide to form ArB *' arche ^ onium 



5o8 



MORPHOLOGY. 



ize the embryo which pushes its way into the endosperm from which it 
derives its food (fig. 362). 

626. Homology of the parts of the female cone. — Opinions are divided as 
to the homology of the parts of the female cone of the pine. Some consider 
the entire cone to be homologous with a flower of the angiosperms. The 




Fig. 361. 
Archegonium of white pine at stage of fertilization, en, egg nucleus; spn, sperm 
nucleus in conjugation with it; nb, nutritive bodies in cytoplasm of large egg; 
cpt, cavity of pollen tube; vn, vegetative nucleus or tube nucleus; sc, stalk cell: 
spn, second sperm nucleus: pr, portion of prothallium or endosperm; sg, starch 
grains in pollen tube. The sheath of jacket cells of the archegonium is not shown. 
(After Ferguson.) 

entire scale according to this view is a carpel, or sporophyll, which is divided 
into the cover scale and the ovuliferous scale. This division of the sporo- 
phyll is considered similar to that which we have in isoetes, where the spo- 
rophyll has a ligule above the sporangium, or as in ophioglossum, where the 
leaf is divided into a fertile and a sterile portion. 

Others believe that the ovuliferous scale is composed of two leaves situ- 
ated laterally and consolidated representing a shoot in the axis of the bract. 
There is some support for this in the fact that in certain abnormal cones 
which show proliferation a short axis appears in the axil of the bract and 



GYMNOSPERMS: WHITE PINE. 



309 



bears lateral leaves, and in some cases all gradations are present between 
these lateral leaves on the axis and their consolidation into an ovuliferous 
scale. In the normal condition of the ovuliferous scale the axis has disap- 
peared and the shoot is represented only by the consolidated leaves, which 
would represent then the 
macrosporophylls (or carpels) 
each bearing one macrospo- 
rangium (ovule). 

One of the most interesting 
and plausible views is that 
of Celakovsky. He believes 
that the axial shoot is reduced 
to two ovules, that the ovules 




Fig. 362. 
Pine seed, section of. sc, 
seed coat ; n , remains of nu- 
cellus ; end, endosperm 
(=female gametophyte); 
emb, embryo = young spo- 
rophyte. Seed coat and 
nucellus= remains of old 
sporophyte. 



Fig. 363- 
Embryo of white 
pine removed from 
seed, showing 
several cotyle- 
dons. 




Fig. 364- 
Pine seedling just 
emerging from the 
ground. 



have two integuments, but the outer integument of each has become pro- 
liferated into scales which are consolidated. In this proliferation of the 
outer integument it is thrown off from the ovule so that it only remains 
attached to one side and the larger part of the ovule is thus left with only 
one integument. This view is supported by the fact that in gingko, for 
example (another gymnosperm), the outer integument (the "collar") 
sometimes proliferates into a leaf. Ceiakovsky's view is, therefore, not 
very different from the second one mentioned above. 



3'Q 



MORPHOLOGY. 




Fig- 365. 
White-pine seedling casting seed coats. 



CHAPTER XXXIV. 



FURTHER STUDIES ON GYMNOSPERMS. 



Cycas. 



627. In such gymnosperms as cycas, illustrated in the front- 
ispiece, there is a close resemblance to the members of the fern 

group, especially the ferns themselves. 
This is at once suggested by the form of 
the leaves. The stem is short and thick. 
The leaves have a stout midrib and 
numerous narrow pinnae. In the center 
of this rosette of leaves are numerous 
smaller leaves, closely overlapping like 
bud scales. If we remove one of these 
at the time the fruit is forming we see that 
in general it conforms to the plan of the 
large leaves. There are a midrib and a 
number of narrow pinnae near the free 
end, the entire leaf being covered with 
woolly hairs. But at the lower end, in 
place of the pinnae, we see oval bodies. 
These are the macrosporangia (ovules) 

of cycas, and correspond to the macrosporangia of selaginella, 

and the leaf is the macrosporophyll. 

628. Female prothallium of cycas. — In figs. 367, 368, are 
shown mature ovules, or macrosporangia, of cycas. In 368, which 
is a roentgen-ray photograph of 367, the oval prothallium can be 
seen. So in cycas, as in selaginella, the female prothallium is 

311 




Fig. 366 
Macrosporophyll 
revoluta. 



of Cycas 



312 



MORPHOLOG Y. 



developed entirely inside of the macrosporangium, and derives 
the nutriment for its growth from the cycas plant, which is the 




Fig. 367. 
Macrosporangium of Cycas revoluta. 



Fig. 368. 
Roentgen photograph of same, show- 
ing female prothallium. 



sporophyte. Archegonia are developed in this internal mass of 
cells. This aids us in deter- 
mining that it is the prothal- 
lium. In cycas it is also called 
endosperm, just as in the 
pines. 

629. If we cut open one of the 
mature ovules, we can see the en- 
dosperm (prothallium) as a whitish 
mass of tissue. Immediately sur- 
rounding it at maturity is a thin, 
papery tissue, the remains of the 
nucellus (macrosporangium), and 
outside of this are the coats of the 
ovule, an outer fleshy one and an 
inner stony one. 

630. Microspores, or pollen, of 

cycas. — The cycas plant illustrated 

in the frontispiece is a female plant. 

Male plants also exist which have 

111 ^ ., . , groups on the under side. 6, group of sporangia; 

small leaves in the center that bear* open sporangia. (From Warming.) 




big 369. 
A sporophyll (stamen) of cycas ; sporangia in 



FURTHER STUDIES ON GYMNOSPERMS. 



313 




only microsporangia. These leaves, while they resemble the ordinary leaves, 
are smaller and correspond to the stamens. Upon 
the under side, as shown in fig. 369, the microspo- 
rangia are borne in groups of three or four, and these 
contain the microspores, or pollen grains. The ar- 
rangement of these microsporangia on the under side 
of the cycas leaves bears a strong resemblance to the 
arrangement of the sporangia on the under side of 
the leaves of some ferns. 

631. The gingko tree is 
another very interesting plant 
belonging to this same group. 
It is a relic of a genus which _ Fig. 370. 

Zamia inte- 
grifolia,show- 
ing thick 
stem, fern-like 
leaves, and 
cone of male 
flowers. 

flourished in the remote 
past, and it is interesting 
also because of the re- 
semblance of the leaves 
to some of the ferns like 
adiantum, which sug- 
gests that this form of 
the leaf in gingko has 
been inherited from some 
fern-like ancestor. 

632. While the resem- 
blance of the leaves of 
some of the gymnosperms 
to those of the ferns sug- 
gests fern-like ancestors 
for the members of this 
group, there is stronger 
evidence of such ances- 
try in the fact that a pro- 
thallium can well be de- 
termined in the ovules. 
The endosperm with its 

well-formed archegonia is to be considered a prothallium. 

633. Spermatozoids in some gymnosperms. — But within the past two 

years it has been discovered in gingko, cycas, and zamia, all belonging to this 



Fig. 371. 
Two spermatozoids in end of pollen tube of cycas. 
drawing by Hirase and Ikeno.) 



(After 



3»4 



MORPHOLOGY. 



group, that the sperm cells are well-formed spermatozoids. In zamia each 
one is shaped somewhat like the half of a biconvex lens, and around the con- 
vex surface are several coils of cilia. After the 
pollen tube has grown down through the nucel- 
lus, and has reached a depression at the end of 
the prothallium (endosperm) where the arche- 
gonia are formed, the spermatozoids are set 
free from the pollen tube, swim around in a 
liquid in this depression, and later fuse with 
the egg. In gingko and cycas these spermato- 
zoids were first discovered by Ikeno and Hirase 
in Japan, and later in zamia by Webber in this 
country. In figs. 371-374 the details of the 
male prothallia and of fertilization are shown. 

634. The sporophyte in the gymnosperms. — 
In the pollen grains of the gymnosperms we 

easily recognize the characters belonging to the 
FlsT- 3 7 2. 
T-, ~. r , • ' .' spores in the ferns and their allies, as well as in 

fertilization m cycas, r ' 

small spermatozoid fusing the liverworts and mosses. They belong to the 

with the larger female nil- , , .« 

cleus of the egg. The egg same series of organs, are borne on the same 

^^W^^&% phase or generation of the plant, and are practi- 
Hirase and Ikeno.) cally formed in the same general way, the 

variations between the different groups not being greater than those within 
a single group. These spores we have recognized as being the product of 
the sporophyte. We are able then to identify the sporophyte as that phase 
or generation of the plant formed from the fer- 
tilized egg and bearing ultimately the spores. 
We see from this that the sporophyte in the 
gymnosperms is the prominent part of the 
plant, just as we found it to be in the ferns. 
The pine tree, then, as well as the gingko, cycas, 
yew, hemlock-spruce, black spruce, "the giant ^Jn^^itJ^l 

a tail. (After Ikeno and 

Hirase.) 





Fig. 373- 



redwood of California, etc., are sporophytes. 

While the sporangia (anther sacs) of the male 
flowers open and permit the spores (pollen) to be scattered, the sporangia of 
the female flowers of the gymnosperms rarely open. The macrospore is de- 
veloped within sporangium (nuccllus) to form the female prothallium (en- 
dosperm). 

635. The gametophyte has become dependent on the sporophyte. — In this 
respect the gymnosperms differ widely from the pteridophytes, though we see 
suggestions of this condition of things in Isoetes and Selaginella, where the fe- 
male prothallium is developed within the macrospore, and even in Selaginella 
begins, and nearly completes, its development while still in the sporangium. 



FURTHER STUDIES ON GYMNOSPERMS. 



315 



In comparing the female prothallium of the gymnosperms with that of the 
fern group we see a remarkable change has taken place. The female pro- 

thallfcim of the gymno- 



Ex 




Fig. 374- 



sperms is very much 
reduced in size. Espe- 
cially, it no longer leads 
an independent existence 
from the sporophyte, as 
is the case with nearly 
all the fern group. It 
remains enclosed within 
the macrosporangium (in 
cycas if not fertilized it 
sometimes grows outside 
of the macrosporangium 
and becomes green), and 
derives its nourishment 
through it from the sporo- 
phyte, to which the latter 
remains organically con- 
nected. This condition 
of the female prothallium 
of the gymnosperms 
necessitated a special 



Gingko biloba. A, mature pollen grain ; B, germinating adaptation of the male 
pollen grain, the branched tube entering among the cells nrnr V, a 11i lirn ; n order that 
of the nucellus; Ex, exine (outer wall of spore); P u pro- P rotnalllum m omer tna t 
thallial cell ; P it antheridial cell (divides later to form stalk the sperm cells may reach 
cell and generative cell) ; P 3 , vegetative cell ; Va, vacuoles ; 
Nc, nucellus. (After drawings by Hirase and Ikeno.) and fertilize the egg cell. 




Fig- 375- 

Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche- 
gonium in the end of the nucellus. pt, pollen tube ; o, archegonium. (After drawing by 
Hirase and Ikeno.) 



636. Gymnosperms are naked seed plants. — The pine, as we have seen, 
has naked seeds. That is, the seeds are not enclosed within the carpel, but 



3i6 



MORPHOLOGY. 



are exposed on the outer surface 




Fig. 376. 
Spermatozoids of 
zami 1 in pollen tube ; 
pg, pollen grain; a, a, 
spermatozoids. (After 
Webber.) 

coordinate with them, 
as follows: 



All the plants of the great group to 
which the pine belongs have 
naked seeds. For this reason 
the name " gymno sperms" 
has been given to this great 
group. 

637. Classification of gymno- 
sperms. — The gingko tree has 
until recently been placed with 
the pines, yew, etc., in the order 
Pinales, but the discovery of 
the spermatozoids in the pollen 
tube suggests that it is not 
closely allied with the Pinales, 
and that it represents an order 
Engler arranges the living gymnosperms somewhat 



Fig. 377. 
Spermatozoid of za- 
mia showing spiral 
row of cilia. (After 
Webber.) 



Order 1. 
Order 2. 
Order 3. 



Class Gymnospermae. 

Cycadales; family Cycadaceae. Cycas, Zamia, etc. 



Gingkoales; family Gingkoaceae. Gingko. 

Pinales (or Conif era?); family 1. Taxacese. Taxus, the common 

yew in the eastern United 
States, and Torreya, in the 
western United States, are 
examples, 
family 2. Pinaceae. Sequoia (redwood of 
California), firs, spruces, pines, 
cedars, cypress, etc. 
Order 4. Gnetales. Welwitschia mirabilis, deserts of southwest Africa; 
Ephedra, deserts of the Mediterranean and of West 
Asia. Gnetum, climbers (Lianas), from tropical 
Asia and America. 



FURTHER STUDIES ON GYMNOSPERMS. 



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CHAPTER XXXV. 

MORPHOLOGY OF THE ANGIOSPERMS : TRILLIUM; 
DENTARIA. 

Trillium. 

639. General appearance. — As one of the plants to illustrate 
this group we may take the wake-robin, as it is sometimes called, 
or trillium. There are several species of this genus in the 
United States; the commonest one in the eastern part is the 
"white wake-robin" (Trillium grandiflorum). This occurs in 
or near the woods. A picture of the plant is shown in fig. 378. 
There is a thick, fleshy, underground stem, or rhizome as it is 
usually called. This rhizome is perennial, and is marked by 
ridges and scars. The roots are quite stout and possess coarse 
wrinkles. From the growing end of the rhizome each year the 
leafy, flowering stem arises. This is 20— 30cm (8-12 inches) in 
height. Near the upper end is a whorl of three ovate leaves, 
and from the center of this rosette rises the flower stalk, bearing 
the flower at its summit. 

640. Parts of the flower. Calyx. — Now if we examine 
the flower we see that there are several leaf- like structures. 
These are arranged also in threes just as are the leaves. First 
there is a whorl of three, pointed, lanceolate, green, leaf-like 
members, which make up the calyx in the higher plants, and the 
parts of the calyx are sepals, that is, each leaf-like member is a 
sepal. But while the sepals are part of the flower, so called, we 
easily recognize them as belonging to the leaf series. 

318 



ANGIOSPERMS: TRILLIUM. 319 

641. Corolla. — Next above the calyx is a whorl of white or 




pinkish members, in 
are also leaf-like in form, 
being usually somewhat 
make up what is the 
and each member of the 
they are parts of the 
their form and posi- 
also belong to the leaf 
642. Andrcecium. — 
tion of the corolla is 
of members which do not 
form. They are known 
As seen in fig. 379 each 
ament), and extending 
greater part of the length 
side. This part of the 
ridges form the anther 
Soon after the flower is 
ther sacs open also by a 
along the edge of the 
time we see quantities of 
or dust escaping from the 



Trillium grandi riorum, which 
and broader than the sepals, 
broader at the free end. These 
corolla in the higher plants, 
corolla is a petal. But while 
flower, and are not green, 
tion would suggest that they 
series. 

Within and above the inser- 

found another tier, or whorl, 

at first sight resemble leaves in 

in the higher plants as stamens. 

stamen possesses a stalk ( = fil- 

along on either side for the 

are four ridges, two on each 

stamen is the a?ither, and the 

sacs, or lobes. 

opened, these an- 

split in the wall 

ridge. At this 

yellowish powder 

Trillium grandiflorum. ruptured anther 




locules. If we place some of this under the microscope we see 



:— 






.... - esi . - . . - 

.... 

- . . - . . . *$ . . - 




4 N 



V 



64S, The stamen a sporo- 
phyll. > noe these 

- 

.- . S - - .- 

s s . tfe scattw 

then we set so . 
Mr sacs, s . . . aoe the spores 

. - . . . - . . 

. . . . s . - 

. . SI 1 - 

UK JUSt SIS - . . 

.■ .• . . ^ . ■ -. 
is believe .... 

^ - 'him. 

644. Gynttcium Next 

. s • 
s - . - - 



1 1 




i 

- 

. - 
- 



A NGIOSPER MS : TRIL LIUM. 



321 



present the only suggestion which it gives of belonging to the 
leaf series is the fact that the end is divided into three parts, the 
number of parts in each successive whorl of members of the 
flower. If we cut across the body of this pistil and examine it 
with a low power we see that there are three chambers or cavi- 
ties, and at the junction of each 
the walls suggest to us that this 
body may have been formed by the 
infolding of the margins of three 
leaf-like members, the places of 
contact having then become grown 
together. We see also that from 
the incurved 
margins of each 
division of the 
pistil there stand 

out in the cavity oval bodies. 
These are the ovules. Now the 
ovules we have learned from our 
study of the gymnosperms are the 
sporangia (here the macrosporangia). 
It is now more evident that this curious body, the. pistil, is made up 
of three leaf-like members which have fused together, each mem- 
ber being the equivalent of a sporophyll (here the macrosporo- 
phyll) . This must be a fascinating observation, that 
plants of such widely different groups and of such 
different grades of complexity should have members 
formed on the same plan and belonging to the same 
series of members, devoted to similar functions, and 
yet carried out with such great modifications that at 
first we do not see this common meeting ground 
which a comparative study brings out so clearly. 

645. Transformations of the flower of trillinm. — 
If anything more were needed to make it clear that 
the parts of the flower of trillium belong to the leaf 
series we could obtain evidence from the transformations which 





Fig. 382. 
Transformed 
stamen of tril- 
lium shoWtng 
anther locules 
on the margin. 



322 MORPBOLOG Y. 

the flower of trillium sometimes presents. In fig. 381 is a sketch 
of a flower of trillium, made from a photograph. One set of 
the stamens has expanded into petal-like organs, with the anther 
sacs on the margin. In fig. 380 is shown a plant of Trillium 
grandiflorum in which the pistil has separated into three distinct 
and expanded leaf-like structures, all green except portions of 
the margin. 



Dentaria. 

646. General appearance. — For another study we may take 
a plant which belongs to another division of the higher plants, 
the common "pepper root," or " toothwort " (Dentaria 
diphylla) as it is sometimes called. This plant occurs in moist 
woods during the month of May, and is well distributed in the 
northeastern United States. A plant is shown in fig. 383. It 
has a creeping underground rhizome, whitish in color, fleshy, 
and with a few scales-. Each spring the annual flower-bearing 
stem rises from one of the buds of the rhizome, and after the 
ripening of the seeds, dies down. 

The leaves are situated a little above the middle point of the 
stem. They are opposite and the number is two, each one 
being divided into three dentate lobes, making what is called a 
compound leaf. 

647. Parts of the flower. — The flowers are several, and they 
are borne on quite long stalks (pedicels) scattered over the ter- 
minal portion of the stem. We should now examine the parts 
of the flower beginning with the calyx. This we can see, look- 
ing at the under side of some of the flowers, possesses four scale- 
like sepals, which easily fall away after the opening of the flower. 
They do not resemble leaves so much as the sepals of trillium, 
but they belong to the leaf series, and there are two pairs in the 
set of four. The corolla also possesses four petals, which are more 
expanded than the sepals and are whitish in color. The sta- 
mens are six in number, one pair lower than the others, and also 



ANGIOSPERMS: DENTARIA. 323 

shorter. The filament is long in proportion to the anther, the 




latter consisting of two 
lobes or sacs, instead of 
four as in trillium. The 
pistil is composed of two 
carpels, or leaves fused 
together. So we find in 
the case of the pepper 
root that the parts of the 
flower are in twos, or 
multiples of two. Thus 
they agree in this respect 
with the leaves ; and 
while we do not see 
such a strong resem- 
blance between the 
parts of the flower 
here and the leaves, 
yet from the pres- 
ence of the pollen 



Fig 383. 
Toothwort (Dentaria diphylla). 



324 



MORPHOLOGY. 



(microspores) in the anther sacs (microsporangia) and of ovules 
(macrosporangia) on the margins of each half of the pistil, we 
are, from our previous studies, able to recognize here that all the 
members of the flower belong to the leaf series. 

648. In trillium and in the pepper root we have seen that the 
parts of the flower in each apparent whorl are either of the same 
number as the leaves in a whorl, or some multiple of that num- 
ber. This is true of a large number of other plants, but it is not 
true of all. A glance at the spring beauty (Claytonia virginiana, 
and at the anemone (or Isopyrum biternatum, fig. 563) will 
serve to show that the number of the different members of the 
flower may vary. The trillium and the dentaria were selected 
as being good examples to study first, to make it very clear that 
the members of the flower are fundamentally leaf structures, or 
rather that they belong to the same series of members as do the 
leaves of the plant. 

649. Synopsis of members of the sporophyte in angiosperms. 

Higher plant. 
Sporophyte phase 
(or modern phase). 



\ Root. 
I Shoot. 



Stem. 
Leaf. 



Foliage leaves. 
Perianth leaves. 
Spore-bearing leaves 

with sporangia. 
(Sporangia sometimes 

on shoot.) 



, Flower. 



CHAPTER XXXVI. 

GAMETOPHYTE AND SPOROPHYTE OF ANGIO- 
SPERMS. 




650. Male prothallium of angiosperms. — The first division 
which takes place in the nucleus of the pollen grain occurs, in 
the case of trillium and many others of the angio- 
sperms, before the pollen grain is mature. In the 
case of some specimens of T. grandiflorum in 
which the pollen was formed during the month 
of October of the year before flowering, the divi- 
Neariy mature sion of the nucleus into two nuclei took place 
Hum. i he smaller soon after the formation of the four cells from 

cell is the genera- . . .. . , , . 

tiveceii. the mother cell. Ine nucleus divided in the 

young pollen grain is shown in fig. 385. After this takes 
place the wall of the pollen grain becomes stouter, and minute 
spiny projections are formed. 

651. The larger cell is the vegetative cell 

of the prothallium, while the smaller one, since 

it later forms the sperm cells, is the generative 

cell. This generative cell then corresponds 

to the central cell of the antheridium, and the 

vegetative cell perhaps corresponds to a wall F - 

cell of the antheridium. If this is so, then the Germinating spores 

male prothallium of angiosperms has become (P°J] en grams) of pel- 
r & r tandra ; generative 

reduced to a very simple antheridium. The nucleus in one undi- 
r ., ,, , , , ~ r ,.,. ,. vided, in other divided 

farther growth takes place alter fertilization, to form the two sperm 

In some plants the generative cell divides into nuclei . 5 vegetative nu- 
r & cleus m each near the 

the two sperm cells at the maturity of the pollen grain. 

pollen grain. In other cases the generative cell divides in the pollen tube 

after the germination of the pollen grain. For study of the pollen tube the 

pollen may be germinated in a weak solution of sugar, or on the cut surface 

325 




326 



MORPHOLOG Y. 



of pear fruit, the latter being kept in a moist chamber to prevent drying 
the surface. 

652. In the spring after flowering the pollen escapes from the anther sacs, 
and as a result of pollination is brought to rest on the stigma of the pistil. 
Here it germinates, as we say, that is, it develops a long tube which makes 
its way down through the 
style, and in through the 
micropyle to the embryo sac, 
where, in accordance with 
what takes place in other 
plants examined, one of the 
sperm cells unites with the 
egg, and fertilization of the 
egg is the result. 



653. Macrospore and embryo sac. 

three carpels are united into one, 
two carpels are also united into one 
Simple pistils are found in many 
in the ranunculaceae, the buttercups, 
These simple pistils bear a greater 




-In trillium the 
and in dentaria the 
compound pistil, 
plants, for example 
columbine, etc. 
resemblance to a 
leaf, the margins of 
which are folded 
around so that they 
meet and enclose 
the ovules or spo- 
rangia. 

654. If we cut 
across the com- 
pound pistil of tril- 
lium we find that 
the infoldings of the 
three pistils meet to 
form three partial 
partitions which 
extend nearly to the center, dividing off three spaces. In these 
spaces are the ovules which are attached to the infolded margins. 
If we make cross sections of a pistil of the May-apple (podo- 




Fig. 387 



Section of pistil of tril- 
lium , showing position of 
ovules (macrosporangia). 



Fig. 388. 
Mandrake (Podo- 
phyllum peltatum). 



GAMETOPHYTE AND SPOROPHYTE. 



327 



phyllum) and through the ovules when they are quite young, we 
shall find that the ovule has a structure like that shown in fig. 389. 
At m is a cell much larger than the surrounding ones. This is 
called the macrospore. The tissue surrounding it is called here the 
nucellus, but because it contains the macrospore it must be the 
macrosporangium. The two coats or integuments of the ovule are 
yet short and have not grown out over the end of the nucellus. 
This macrospore increases in size, forming first a cavity or sac 
in the nucellus, the embryo sac. The nucleus divides several 




Fig. 389. 
Young ovule (macrosporangium) of podophyllum, n, nucellus containing the one- 
celled stage of the macrospore; i.int, inner integument; o.int, outer integument. 

times until eight are formed, four in the micropylar end of the 
embryo sac and four in the opposite end. In some plants it 
has been found that one nucleus from each group of four moves 
toward the middle of the embryo sac. Here they fuse together 
to form one nucleus, the endosperm nucleus or definitive nucleus 
shown in fig. 390. One of the nuclei at the micropylar end is 
the egg, while the two smaller ones nearer the end are the syner- 



328 



MORPHOLOG Y. 



gids. The egg cell is all that remains of the archegonium in 
this reduced prothallium. The three nuclei at the lower end 
are the antipodal cells. 




Fig. 390. 
Podophyllum peltatum, ovule containing mature embryo sac; two synergids and 
eggs at left, endosperm nucleus in center, three antipodal cells at right. 

655. Embryo sac is the young female prothallium.— In figs. 
39 J "3 93 are shown the different stages in the development of 

the embryo sac in lilium. The 
embryo sac at this stage is the 
young female prothallium, and 
the egg is the only remnant of the 
female sexual organ, the arche- 
gonium, in this reduced gameto- 
phyte. 

656. Fertilization.— When the 
pollen tube has reached the em- 
bryo sac (paragraph 652) it opens 
Macrospore (one-ceiled stage) of lilium. anc i tne t wo sperm cells are emptied 
near the egg. The first sperm nucleus enters the protoplasm 
surrounding the egg nucleus and uniting with the latter brings 
about fertilization. The second sperm nucleus often unites 
with the endosperm nucleus (or with one or both of the "polar 
nuclei"), bringing about what some call a second fertilization. 
Where this takes place in addition to the union of the first sperm 




Fig. 391. 



GAMETOPHYTE AND SPOROPHYTE. 



329 



nucleus with the egg nucleus it is called double fertilization. The 
sperm nucleus is usually smaller than the egg nucleus, but often 
grows to near or quite the size of the egg nucleus before union. 
See figs. 394 and 395. 

657. Fertilization in plants is fundamentally the same as 
in animals. — In all the great groups of plants as represented by 
spirogyra, cedogonium, vaucheria, peronospora, ferns, gymno- 





rale 



m 

*«.«,, 




Fig. 392. 
Two- and four-celled stage of embryo-sac of lilium. The middle one shows 
division of nuclei to form the four-celled stage. (Easter lily.) 

sperms, and in the angiosperms, fertilization, as we have seen, 
consists in the fusion of a male nucleus with a female nucleus. 
Fertilization then, in plants is identical with that which takes 
place in animals. 

658. Embryo. — After fertilization the egg develops into a short 
row of cells, the sus pernor of the embryo. At the free end the em- 
bryo develops. In figs. 397 and 398 is a young embryo of trillium. 

659. Endosperm, the mature female prothallium. — During 
the development of the embryo the endosperm nucleus divides 



330 



MORPHOLOGY. 



into a great many nuclei in a mass of protoplasm, and cell walls 
are formed separating them into cells. This mass of cells is the 
endosperm, and it surrounds the 
embryo. It is the mature female 
prothallium, belated in its growth 
in the angiosperms, usually de- 
veloping only when fertilization 
takes place, and its use has been 
assured. 

660. Seed. — As the embryo 





Fig. 393- 

Mature embryo sac (young pro- 
thallium) of lilium. m, micropylar 
end ; 5, synergids ; E, egg ; P?i, 
polar nuclei; Ant, antipodals. 
(Easter lily.) 



Fig- 394- 

Section through nucellus and upper part of embryo 
sac of cotton at time of entrance of pollen tube. E, 
egg; S, synergids; P, pollen tube with sperm cell in 
the end. (Duggar.) 



GAMETOPHYTE AND SPOROPHYTE. 



33 



is developing it derives its nourishment from the endosperm (or 
in some cases perhaps from the nucellus). At the same time 





Fig- 395- 
Fertilization of cotton, 
pollen tube; Sn, synergids ; 
egg, with male and female 
cleus fusing. (Duggar.) 

the integuments increase 
in extent and harden as < 
the seed is formed. 

661. Perisperm. — In 
most plants the nucellus is ax 
all consumed in the devel- 
opment of the endosperm, 
so that only minute frag- 
ments of disorganized cell 
walls remain next the in- 
ner integument. In some 
plants, however, (the water- 
lily family, the pepper TV . ps-3 9 6. 

J J7 r rr Diagrammatic section of ovary and ovule at time 

family, etc.,) a portion Of of fertilization in angiosperm. f, funicle of ovule ; 

J7 '/ r n, nucellus; in, micropyle ; o, antipodal cells or 

the nucellus remains in- embryo sac ; e, endosperm nucleus ; /-egg cell and 

synergids ; at, outer integument of ovule ; z/, inner 
tact in the mature Seed, integument. The track of the pollen tube is shown 

down through the style, walls of the ovary to the 

In such seeds the remain- mkropyiar end of the embryo sac . 
ing portion of the nucellus is the perisperm. 

662. Presence or absence of endosperm in the seed. — In 
many of the angiosperms all of the endosperm is consumed by 
the embryo during its growth in the formation of the seed. This 
is the case in the rose family, crucifers, composites, willows, oaks, 
legumes, etc., as in the acorn, the bean, pea and others. In 
some, as in the bean, a large part of the nutrient substance pass- 



332 



MORPHOLOGY. 



ing from the endosperm into the embryo is stored in the cotyle- 
dons for use during germination. In other plants the endosperm 




Fig. 397- Fig. 398. 

Section of one end of ovule of trillium, showing Embryo e n - 

young embryo in endosperm. larged. 

is not all consumed by the time the seed is mature. Examples of 
tins kind are found in the buttercup family, the violet, lily, palm, 





Fig. 399- 
Seed of violet, external view, and 
section. The section shows the embryo 
lying in the endosperm. 




Fig. 400. 
Section of fruit of pepper (Piper 
nigrum), showing small embryo lying 
in a small quantity of whitish endo- 
sperm at one end, the perisperm oc- 
cupying the larger part of the interior, 
surrounded by pericarp. 



jack-in-the-pulpit, etc. Here the remaining endosperm in the 
seed is used as food by the embryo during germination. 
663. Outer parts of the seed. — While the embryo is forming 



ANGIOSPERMS : SEED. . 333 

within the ovule and the growth of the endosperm is taking 
place, where this is formed, other correlated changes occur in 
the outer parts of the ovule, and often in adjacent parts of the 
flower. These unite in making the " seed, " or the " fruit. " 
Especially in connection with the formation of the seed a new 
growth of the outer coat, or integument, of the ovule occurs, 
forming the outer coat of the seed, known as the testa, while 
the inner integument is absorbed. In some cases the inner 
integument of the ovule also forms a new growth, making an 
inner coat of the seed (rosaceae). In still other cases neither 
of the integuments develops into a testa, and the embryo sac 
lies in contact with the wall of the ovary. Again an additional 
envelope grows up around the seed; an example of this is 
found in the case of the red berries of the " yew " (taxus), the 
red outer coat being an extra growth, called an aril. 

In the willow and the milkweed an aril is developed in the 
form of a tuft of hairs. (In the willow it is an outgrowth of 
the funicle, = stalk of the ovule, and is called a funicular aril; 
while in the milkweed it is an outgrowth of the micropyle, = 
the open end of the ovule, and is called a micropylar aril.) 

664. Increase in size during seed formation. — Accompany- 
ing this extra growth of the different parts of the ovule in the 
formation of the seed is an increase in the size, so that the seed 
is often much greater in size than the ovule at the time of fer- 
tilization. At the same time parts of the ovary, and in many 
plants, the adherent parts of the floral envelopes, as in the apple; 
or of the receptacle, as in the strawberry; or in the involucre, 
as in the acorn; are also stimulated to additional growth, and 
assist in making the fruit. 



334 



MORPHOLOGY. 



Ripened, ovule. 



The seed,. ■< 



665. Synopsis of the seed. 

Aril, rarely present. 

Ovular coats (one or two usually present), the 

testa. 
Funicle (stalk of ovule), raphe (portion of 
funicle when bent on to the side of ovule), 
micro pyle, hilum (scar where seed was 
attached to ovary). 
Remnant of the nucellus (central part of 

ovule); sometimes nucellus remains as 
Perisperm in some albuminous seeds. 
Endosperm, present in albuminous seeds. 

Embryo within surrounded by endosperm when this is present, 
or by the remnant of nucellus, and by the ovular coats which 
make the testa. In many seeds (example, bean) the endo- 
sperm is transferred to the cotyledons which become fleshy 
(exalbuminous seeds). 

666. Parts of the ovule. — In fig. 401 are represented three 
different kinds of ovules, which depend on the position of the 




Fig. 401. 
A, represents a straight (orthotropus) ovule of polygonum; B, the inverted 
(anatropous) ovule of the lily; and C, the right-angled (campylotropus) ovule of 
the bean, f, funicle; c, chalaza; k, nucellus; ai, outer integument; ii, inner 
integument; m, micropyle; em, embryo sac. 

ovule with reference to its stalk. The funicle is the stalk of the 
ovule, the hilum is the point of attachment of the ovule with 
the ovary, the raphe is the part of the funicle in contact with 
the ovule in inverted ovules, the chalaza is the portion of the 
ovule where the nucellus and the integuments merge at the base 
of the ovule, and the micropyle is the opening at the apex of 
the ovule where the coats do not meet. 



FL O WER : MEMBERS A ND ORG A NS. 335 



Comparison of Organ and Member. 

667. The stamens and pistils are not the sexual organs. — 

Before the sexual organs and sexual processes in plants were 
properly understood it was customary for botanists to speak 
of the stamens and pistils of flowering plants as the sexual 
organs. Some of the early botanists, a century ago, found that 
in many plants the seed would not form unless first the pollen 
from the stamens came to be deposited on the stigma of the 
pistil. A little further study showed that the pollen germinated 
on the stigma and formed a tube which made its way down 
through the pistil and into the ovule. 

This process, including the deposition of the pollen on the 
stigma, was supposed to be fertilization, the stamen was looked 
on as the male sexual organ, and the pistil as the female sexual 
organ. We have found out, however, by further study, and 
especially by a comparison of the flowering plants and the lower 
plants, that the stamens and pistils are not the sexual organs of 
the flower. 

668. The stamens and pistils are spore-bearing leaves. — The 
stamen is the spore-bearing leaf, and the pollen grains are not 
unlike spores; in fact they are the small spores of the angio- 
sperms. The pistil is also a spore-bearing leaf, the ovule the 
sporangium, which contains the large spore called an embryo sac. 
In the ferns we know that the spore germinates and produces the 
green heart-shaped prothallium. The prothallium bears the 
sexual organs. Now the fern leaf bears the spores and the spore 
forms the prothallium. So it is in the flowering plants. The 
stamen bears the small spores — pollen grains — and the pollen 
grain forms the prothallium. The prothallium in turn forms 
the sexual organs. The process is in general the same as it is in 
the ferns, but with this special difference: the prothallium and 
the sexual organ of the flowering plants are very much reduced. 

669. Difference between organ and member. — While it is 
not strictly correct then to say that the stamen is a sexual organ, 



3 $6 MORPBOL OGY. 

or male organ, we might regard it as a male member of the flower, 
and we should distinguish between organ and member. It is an 
organ when we consider pollen production, but it is not a sexual 
organ. When we consider fertilization it is not a sexual organ, 
but a male member of the flower which bears the small spore. 
The following table will serve to indicate these relations. 

Stamen = spore-bearing leaf = male member of flower. 

Anther locule = sporangium. 

Pollen grain = small spore = reduced male pro thallium and 
sexual organ. 

So the pistil is not a sexual organ, but might be regarded as 
the female member of the flower. 

Pistil = spore-bearing leaf = female member of flower. 

Ovule = sporangium. 

Embryo sac = large spore = female pro thallium containing the 

egg- 
The egg =a reduced archegonium-=the female sexual organ. 

Progression and Retrogression in Sporophyte and 
Gametophyte. 

670. Sporophyte is prominemt and highly developed. — In the angiosperms 
then, as we have seen from the plants already studied, the trillium, dentaria, 
etc., are sporophytes, that is they represent the spore -bearing, or sporophytic, 
stage. Just as we found in the case of the gymnosperms and ferns, this stage 
is the prominent one, and the one by which we characterize and recognize the 
plant. We see also that the plants of this group are still more highly special- 
ized and complex than the gymnosperms, just as they were more specialized 
and complex than the members of the fern group. From the very simple 
condition in which we possibly find the sporophyte in some of the algae like 
spirogyra, vaucheria, and coleochsete, there has been a gradual increase in 
size, specialization of parts, and complexity of structure through the bryo- 
phytes, pteridophytes, and gymnosperms, up to the highest types of plant 
structure found in the angiosperms. Not only do we find that these changes 
have taken place, but we see that, from a condition of complete dependence of 
the spore-bearing stage on the sexual stage (gametophyte), as we find it in the 
liverworts and mosses, it first becomes free from the gametophyte in the mem- 
bers of the fern group, and is here able to lead an independent existence. 
The sporophyte, then, might be regarded as the modern phase of plant life, 



GAMETOPHYTE AND SPOROPHYTE. 337 

since it is that which has become and remains the prominent one in later 
times. 

671. The gametophyte once prominent has become degenerate. — On the 

other hand we can see that just as remarkable changes have come upon the 
other phase of plant life, the sexual stage, or gametophyte. There is reason 
to believe that the gametophyte was the stage of plant life which in early 
times existed almost to the exclusion of the sporophyte, since the characteristic 
thallus of the algae is better adapted to an aquatic life than is the spore-bearing 
state of plants. At least, we now find in the plants of this group as well as in 
the liverworts, that the gametophyte is the prominent stage. When we reach the 
members of the fern group, and the sporophyte becomes independent, we find 
that the gametophyte is decreasing in size, in the higher members of thepteri- 
dophytes, the male prothallium consisting of only a few cells, while the fe- 
male prothallium completes its development still within the spore wall. And 
in selaginella it is entirely dependent on the sporophyte for nourishment. 

672. As we pass through the gymnosperms we find that the condition of 
things which existed in the bryophytes has been reversed, and the gameto- 
phyte is now entirely dependent on the sporophyte for its nourishment, the 
female prothallium not even becoming free from the sporangium, which remains 
attached to the sporophyte, while the remnant of a male prothallium, during 
the stage of its growth, receives nourishment from the tissues of the nucellus 
through which it bores its way to the egg-cell. 

673. In the angiosperms this gradual degradation of the male and female 
prothallia has reached a climax in a one-celled male prothallium with two 
sperm-cells, and in the embryo-sac with no clearly recognizable traces of an 
archegonium to identify it as a female prothallium. The development of the 
endosperm subsequent, in most cases, to fertilization, providing nourishment 
for the sporophytic embryo at one stage or another, is believed to be the last 
remnant of the female prothallium in plants. 

674. The seed. — The seed is the only important character possessed by 
the higher plants (the gymnosperms and angiosperms) which is not pos* 
sessed by one or another of the lower great groups. With the gradual eve 
lution of the higher plants from the lower there has been developed at cer- 
tain periods organs or structural characters which were not present in some 
of the lower groups. Thus the thallus is the plant body of the algae and 
fungi, so that these two groups of plants are sometimes called Thallophytes. 
In the Bryophytes (liverworts and mosses) the thallus is still present, but 
there is added the highly organized archegonium in place of the simple 
female gamete or oogonium, or carpogonium of the alga? and fungi, and the 
sporophyte has become a distinct though still dependent structure. In the 
Pteridophytes the thallus is still present as the prothallium, archegoina are 
also present, and while both of these structures are retrograding the spo- 
rophyte has become independent and has organized for the first time a true 



33 8 MO RP HO LOG V. 

vascular system for conduction of water and food. In the gymnosperms 
and angiosperms the thallus is present in the endosperm; distinct, though 
reduced, archegonia are present in most gymnosperms and represented 
only by the egg in the angiosperms; the vascular system is still more highly 
developed while the seed for the first time is organized, and characterizes 
these plants so that they are called seed plants, or Spermatophytes. 

Variation, Hybridization, Mutation. 

674a. Variation. — It is a well-known fact that plants as well as ani- 
mals are subject to variation. Under certain conditions, some of which 
are partly understood and others are unknown, the progeny of plants dif- 
fer in one or more characters from their parents. Some of these variations 
are believed to be due to the influence of environment (see Parts III and 
IV). Others are the result of the crossing of individuals which show 
greater or lesser differences in one or more characters, or the crossing of 
different species (hybridization). The most profound variations are those 
which spring suddenly into existence (mutation). 

674b. Hybridization. — Two different species are " crossed' ' where the 
egg-cell of one species is fertilized by the sperm of another species. The 
progeny resulting from such a cross is a hybrid. Hybrids sometimes resem- 
ble one parent, sometimes another, sometimes both. Where the parents 
differ only in respect to one character of an organ or structure, there is a 
regular law in respect to the progeny if they are self-fertilized. In the 
first generation all the individuals are alike and resemble one of the parents, 
and the special differential character of that parent is called the dominant 
character. In the second generation 75% possess the dominant character, 
while 25% resemble the other original parent, and its differential charac- 
ter is called recessive. These are pure recessives, since successive genera- 
tions, if self-fertilized, are always recessive. Of the 75% which show the 
dominant character in the second generation, one-third (or 25% of the 
whole number) are pure dominants if self-fertilization is continued, while 
50% are really "cross breds" like the first generation, and if self -fertilized 
split up again into approximately 25 dominants, 50 cross breds, and 25 
recessives. This is what is called Mendel's law. Where the original par- 
ents differ in respect to more than one character, the result is more compli- 
cated (see Mendel's Principles of Heredity; also de Vries, Das Spaltungs- 
gesetz der Bastarde, Per. d. deutsch. bot. Gesell., 18, 83, 1900). 

674c. Mutation. — This term is applied to those variations which appear 
so suddenly that some of the progeny of two like individuals differ from all 
the others to a marked degree. Some of these mutations are so different 
as to be regarded as new species. Some of the primroses show mutations, 
and (Enothera gigas is a mutation from Oenothera lamarkiana (see de Vries, 
Die Mutationstheorie, Leipzig) 



GAMETOPHYTE AND SPOROPHYTE. 



339 




CHAPTER XXXVII. 



MORPHOLOGY OF THE NUCLEUS AND SIGNIFI- 
CANCE OF GAMETOPHYTE AND SPOROPHYTE. 

676. In the development of the spores of the liverworts, 
mosses, ferns, and their allies, as well as in the development of 
the microspores of the gymnosperms and angiosperms, we have 

observed that four spores are formed 
from a single mother cell. These 





Fig. 402. 
Forming spores in mother 
cells (Polypodium vulgare). 



Fig. 4°3- 
Spores just mature and wall of 
mother cell broken (Asplenium bul- 
biferum). 



mother cells are formed as a last division of the fertile 
tissue (archesporium) of the sporangium. In ordinary cell di- 
vision the nucleus always divides prior to the division of the cell. 
In many cases it is directly connected with the laying down of 
the dividing cell wall. 

677. Direct division of the nucleus. — The nucleus divides in 
two different ways. On the one hand the process is very simple. 
The nucleus simply fragments, or cuts itself in two. This is 
direct division. 

678. Indirect division of the nucleus. — On the other hand 
very complicated phenomena precede and attend the division of 

34o 



GAMETOPHYTE AND SPOROPHYTE. 



)4I 



the nucleus, giving rise to a succession of nuclear figures presented 
by a definite but variable series of evolutions on the part of the 
nuclear substance. This is indirect division of the nucleus, or 
karyokinesis. Indirect division of the nucleus is the usual method, 
and it occurs in the normal growth and division of the cell. The 
nuclear figures which are formed in the division of the mother 
cell into the four spores are somewhat different from those 
occurring in vegetative division, but their study will serve to show 
the general character of the process. 

679. Chromatin and linin of the nucleus. — In figure 404 
is represented a pollen mother cell of the May-apple (podophyl- 




Fig. 404. Fig. 405. Fig. 406. 

Pollen mother cell Spirem stage of nucleus. Forming spindle, 

of podophyllum, rest- nu, nuclear cavity ; n, nu- threads from proto- 

ingnucleus. Chroma- cleolus ; Sp, spirem. plasm with several 

tin forming a net- poles, roping the 

work. chromosomes up to 

(Figures 404-406 after Mottier.) nuclear plate. 

lum). The nucleus is in the resting stage. There is a network 
consisting of very delicate threads, the linin network. Upon 
this network are numerous small granules, and at the junction of 
the threads are distinct knots. The nucleolus is quite large and 
prominent. The numerous small granules upon the linin stain 
very deeply when treated with certain dyes used in differentiating 
the nuclear structure. This deeply staining substance is the 
chromatin of the nucleus. 



342 



MORPHOLOGY. 



680. The chromatin skein. — One of the first nuclear figures 
in the preparatory stages of division is the chromatin skein or 
spirem. The chromatin substance unites to form this. The 
spirem is in the form of a narrow continuous ribbon, or band, 
woven into an irregular skein, or gnarl, as shown in figure 405. 
This band splits longitudinally into two narrow ones, and then 
each divides into a definite number of segments, about eight in 
the case of podophyllum. Sometimes the longitudinal splitting of 
the band appears to take place after the separation into the chro- 
matin segments. The segments remain in pairs until they separate 
at the nuclear plate. 

681. Chromosomes, nuclear plate, and nuclear spindle. — 
Each one of these rod-like chromatin segments is a chromosome. 




Fig. 407. 

Karyokinesis in pollen mother cells of podophyllum. At the left the spindle with the 
chromosomes separating at the nuclear plate ; in the middle figure the chromosomes have 
reached the poles of the spindle, and at the right the chromosomes are forming the daughter 
nuclei. (After Mottier.) 

The pairs of chromosomes arrange themselves in a median plane 
of the nucleus, radiating somewhat in a stellate fashion, forming 
the nuclear plate , or monaster. At the same time threads of the 
protoplasm (kinoplasm) become arranged in the form of a spindle, 
the axis of which is perpendicular to the nuclear plate of chromo- 
somes, as shown in figure 407, at left. Each pair of chromosomes 
now separate in the line of the division of the original spirem, 
one chromosome of each pair going to one pole of the spindle, 



GAMETOPHYTE AND SPOROPHYTE. 



343 





while the other chromosome of each pair goes to the opposite 
pole. The chromosomes here unite to form the daughter nuclei. 

Each of these nuclei now 
divide as shown in figure 
409 (whether the chromo- 
somes in this second divi- 
sion in the mother cell split 
longitudinally or divide 
transversely has not been 
definitely settled), and four 

Different stages in the separation of divided nuc l e i are formed in the 
U-shaped chromosomes at the nuclear plate. (After 

Mottier) in podophyllum. pollen mother cell. The 

protoplasm about each one of these four nuclei now surrounds 
itself with a wall and the spores are formed. 

The number of chromosomes usually the same in a given 
species throughout one phase of" the plant. — In those plants 
which have been carefully studied, the number of chromosomes 
in the dividing nucleus has been found to be fairly constant in a 
given species, through all the divisions in that stage or phase 
of the plant, especially in the embryonic, or young growing 
parts. For example, in the 
prothallium, or gameto- 
phyte, of certain ferns, as 
osmunda, the number of 
chromosomes in the divid- 
ing nucleus is always twelve. 
So in the development of 
the pollen of lilium from 
the mother cells, and in the 
divisions of the antherid 
cell to form the generative 
cells or sperm cells, there 




Fig. 409. 
Second division 



of 



Fig. 41 
Chromosomes uniting 



are alwaVS twelve chroniO- nuc l e | in pollen mother at poles to form the 
^ ^ c e 1 1 of podophyllum, nuclei of the four spores. 

SOmeS SO far as has been chromosomes at poles. (After Mottier.) 

found. In the development of the egg of lilium from the 
macrospore there are also twelve chromosomes. 



344 



MORPHOLOG Y. 



When fertilization takes place the number of chromosomes 
is doubled in the embryo. — In the spermatozoid of osmunda 
then, as well as in the egg, since these are developed on the game- 
tophyte, there are twelve chromosomes each. The same is true 
in the sperm-cell (generative cell) of lilium, and also in the egg- 
cell. When these nuclei unite, as they do in fertilization, the 
paternal nucleus with the maternal nucleus, the number of chro- 
mosomes in the fertilized egg, if we take lilium as an example, 
is twenty-four instead of twelve; the number is doubled. The 
fertilized egg is the beginning of the sporophyte, as we have seen. 
Curiously throughout all the divisions of the nucleus in the em- 
bryonic tissues of the sporophyte, so far as has been determined, 
up to the formation of the mother cells of the spores, the number 
of chromosomes is usually the same 

682. Reduction of the number of chromosomes in the nu- 
cleus. — If there were no reduction in the number of chromosomes 




Fig. 411. 
Karyokinesis in sporophyte cells of podophyllum (twice the number of chromosomes 
here that are found in the dividing spore mother cells). 

at any point in the life cycle of plants, the number would thus 
become infinitely large. A reduction, however, does take place. 



GAMETOPHYTE AND SPOROPHYTE. 345 

This usually occurs, either in the mother cell of the spores or in 
the divisions of its nucleus, at the time the spores are formed. In 
the mother cells a sort of pseudo-reduction is effected by the 
chromatin band separating into one half the usual number of nu- 
clear segments. So that in lilium during the first division of the 
nucleus of the mother cell the chromatin band divides into twelve 
segments, instead of twenty-four as it has done throughout the 
sporophyte stage. So in podophyllum during the first division in 
the mother cell it separates into eight instead of into sixteen. 
Whether a qualitative reduction by transverse division of the 
spirem band, unaccompanied by a longitudinal splitting, takes 
place during the first or second karyokinesis is still in doubt. 
Qualitative reduction does take place in some plants according 
to Beliaieff and others. Recently the author has found that it 
takes place in Trillium grandiflorum during the second karyoki- 
nesis, and in Arisaema triphyllum the chromosomes divide both 
transversely and longitudinally during the first karyokinesis form- 
ing four chromosomes, and a qualitative reduction takes place here. 
• 683. Significance of karyokinesis and reduction. — The pre 
cision with which the chromatin substance of the nucleus is di- 
vided, when in the spirem stage, and later the halves of the 
chromosomes are distributed to the daughter nuclei, has led to the 
belief that this substance bears the hereditary qualities of the 
organism, and that these qualities are thus transmitted with cer- 
tainty to the offspring. In reduction not only is the original 
number of chromosomes restored, it is believed by some that 
there is also a qualitative reduction of the chromatin, i.e. that 
each of the four spores possesses different qualitative elements of 
the chromatin as a result of the reducing division of the nucleus 
during their formation. 

The increase in number of chromosomes in the nucleus occurs 
with the beginning of the sporophyte, and the numerical reduc- 
tion occurs at the beginning of the gametophyte stage. The 
full import of karyokinesis and reduction is perhaps not yet 
known, but there is little doubt that a profound significance is to 
be attached to these interesting phenomena in plant life. 



34-6 



MORPHOLOGY. 



684. The gametophyte may develop directly from the tissue 
of the sporophyte. — If portions of the sporophyte of certain of 
the mosses, as sections of a growing seta, or of the growing 
capsule, be placed on a moist substratum, under favorable condi- 
tions some of the external cells will grow directly into protonemal 
threads. In some of the ferns, as in the sensitive fern (onoclea), 
when the fertile leaves are expanding into the sterile ones, proto- 
nemal outgrowths occur among the aborted sporangia on the 
leaves of the sporophyte. Similar rudimentary protonemal 
growths sometimes occur on the leaves of the common brake 
(pteris) among the sporangia, and some of the rudimentary spo- 
rangia become changed into the protonema. In some other 
ferns, as in asplenium(A. filix-fcemina, var. clarissima), prothallia 
are borne among the aborted sporangia, which bear antheridia 
and archegonia. In these cases the gametophyte develops from 
the tissue of the sporophyte without the intervention or necessity 
of the spores. This is apospory. 

685. The sporophyte may develop directly from the tissue 
of the gametophyte. — In some of the ferns, Pteris cretica for 
example, the embryo fern sporophyte arises directly from the tissue 
of the prothallium, without 
the intervention of sexual 
organs, and in some cases 
no sexual organs are de- 
veloped on such prothallia. 
Sexual organs, then, and 
the fusion of the spermato- 
zoid and egg nucleus are 
not here necessary for the 
development of the spo- 
rophyte. This is apogamy. 
Apogamy occurs in some 
other species of ferns, and 
in other groups of plants as well, though it is in general a rare 
occurrence except in certain species, where it may be the general 
rule. 




Fig. 412. 
Apogamy in Pteris cretica. 



GAMETOPHYTE AND SPOROPHYTE. 347 

686. Types of nuclear division. — The nuclear figures in the 
vegetative cells are usually different from those in the spore 
mother cells. In the spore mother cells there are two types of 
nuclear division, (i) The first division in the mother cell is 
called heterotypic. The early stages of this division usually 
extend over a longer period than the second, and the figures are 
more complex. Before the chromosomes arrive at the nuclear 
plate they are often in the form of rings, or tetrads, or in the 
form of X, V, or Y, and the number is usually one half the num- 
ber in the preceding cells of the sporophyte. (2) The homo- 
typic division immediately follows the heterotypic and the figures 
are simpler, often the chromosomes being of a hook form, or 
sometimes much stouter than in the heterotypic division. In 
the vegetative cells (sometimes called somatic cells, or body 
cells in contrast with reproductive cells) there is another type, 
called by some the vegetative type. The chromosomes here are 
often in the form of the letter U, and the figures are much sim- 
pler than in the heterotypic division. In the somatic cells of 
the sporophyte, as stated above, the number of chromosomes is 
double that found in the heterotypic and homotypic divisions of 
the mother cells and in the somatic cells of the gametophyte, 
Fig. 411 represents a late stage in the division of somatic cells 
in the sporophyte of podophyllum. The root tips of various 
plants as the onion, lily, etc., are excellent places in which to 
study nuclear division in the somatic cells of the sporophyte. 

687. Comparison with animals. — In animals there does not 
seem to be anything which corresponds with the gametophyte of 
plants unless the sperm cells and eggs themselves represent it. 
Heterotypic and homotypic division with the accompanying 
reduction of the number of the chromosomes takes place in ani- 
mals usually in the mother cells of the sperms and eggs. At 
the time of fertilization the number of chromosomes is doubled, 
so that all the somatic cells (except in rare instances) from the 
fertilized egg to the mother cells of sperms and eggs have the 
doubled number of chromosomes. Reduction, therefore, takes 
place in animals just prior to the formation of the gametes, while 



34§ MORPHOLOGY. 

in plants it takes place just prior to the formation of the gameto- 
phytes. 

688. Perhaps there is not a fundamental difference between 
gametophyte and sporophyte. — This development of sporophyte, 
or leafy-stemmed plant of the fern (parag. 685), from the tissue 
of the gametophyte is taken by some to indicate that there is not 
such a great difference between the gametophyte and sporophyte 
of plants as others contend. In accordance with this view it has 
been suggested that the leafy-stemmed moss plant, as well as the 
leafy stem of the liverworts, is homologous with the sporophyte or 
leafy stem of the fern plant; that it arises by budding from the 
protonema; and that the sexual organs are borne then on the 
sporophyte. 



PART III. 

PLANT MEMBERS IN RELATION TO ENVIRONMENT. 

CHAPTER XXXVIII. 

THE ORGANIZATION OF THE PLANT. 

I. Organization of Plant Members.* 

689. It is now generally conceded that the earliest plants to 
appear in the world were very simple in form and structure. 
Perhaps the earliest were mere bits of naked protoplasm, not 



* Suggestions to the teacher, — In the study of the flowering plants in the 
secondary school and in elementary courses three general topics are sug- 
gested, ist, the study of the form and members of the plant and their 
arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few 
plants representative of the more important families, in order that the 
members of the plant, as studied under the first topic, may be seen in corre- 
lation with the plant as a whole in a number of different types. 3d, the 
study of plants in their relation to environment, as in Chapter XLVI. 
The first and second topics can be conducted consecutively in the class- 
room and laboratory. The third topic can be studied at opportune times 
during the progress of topics 1 and 2. For example, while studying topic 1 
excursions can be made to study winter conditions of buds, shoots, etc., 
if in winter period, or the relations of leaves, etc., to environment, if in 
the growing period. While studying topic 2 excursions can be made to 
study flower relations, and also vegetation relations to environment (see 
Chapters XLVI-LVII of the author's "College Text-book of Botany"). 
It is believed that a study of these three general topics is of much more 
value to the beginning student than the ordinary plant analysis and deter- 
mination of species. 

349 



35° RELATION TO ENVIRONMENT, 

essentially different from early animal life. The simplest ones 
which are clearly recognized as plants are found among the 
lower algae and fungi. These are single cells of very minute 
size, roundish, oval, or oblong, existing during their growing 
period in water or in a very moist substratum or atmosphere. 
Examples are found in the red snow plant (Sphcerella nivalis), 
the Pleurococcus, the bacteria; and among small colonies of 
these simple organisms (Pandorina) or the thread-like forms 
(Spirogyra, OEdogonium, etc.). It is evident that some of the 
life relations of such very simple organisms are very easily ob- 
tained — that is, the adjustment to environment is not difficult. 
All of the living substance is very closely surrounded by food 
material in solution. These food solutions are easily absorbed. 
Because of the minute size of the protoplasts and of the plant 
body, they do not have to solve problems of transport of food to 
distant parts of the body. When we pass to more bulky organ- 
isms consisting of large numbers of protoplasts closely com- 
pacted together, the problem of relation to environment and of 
food transport become felt; the larger the organism usually the 
greater are these problems. A point is soon reached at which 
there is a gain by a differentiation in the work of different proto- 
plasts, some for absorption, some for conduction, some for the 
light relation, some for reproduction, and so on. There is also 
a gain in splitting the form of the plant body up into parts so that 
a larger surface is exposed to environment with an economy in 
the amount of building material required. In this differentiation 
of the plant body into parts, there are two general problems to 
be solved, and the plant to be successful in its struggle for exist- 
ence must control its development in such a way as to preserve 
the balance between them, (i) A ready display of a large sur- 
face to environment for the purpose of acquiring food and the 
disposition of waste. (2) The protection of the plant from 
injuries incident to an austere environment. 

It is evident with the great variety of conditions met with in 
different parts of the same locality or region, and in different 
parts of the globe, that the plant has had very complex problems 



ORGANIZATION PLANT MEMBERS. 351 

to meet and in the solution of them it has developed into a great 
variety of forms. It is also likely that different plants would in 
many cases meet these difficulties in different ways, sometimes 
with equal success, at other times with varied success. Just as 
different persons, given some one piece of work to do, are likely 
to employ different methods and reach results that are varied as 
to their value. While we cannot attribute consciousness or 
choice to plants in the sense in which we understand these qual- 
ities in higher animals, still there is something in their " consti- 
tution" or "character" whereby they respond in a different 
manner to the same influences of environment. This is, per- 
haps, imperceptible to us in the different individuals of the same 
species, but it is more marked in different species. Because of 
our ignorance of this occult power in the plant, we often speak of 
it as an "inherent" quality. 

Perhaps the most striking examples one might use to illustrate the dif- 
ferent line of organization among plants in two regions where the environ- 
ment is very different are to be found in the adaptation of the cactus or 
the yucca to desert regions, and the oak or the cucurbits to the land condi- 
tions of our climate. The cactus with stem and leaf function combined in 
a massive trunk, or the yucca with bulky leaves expose little surface in 
comparison to the mass of substance, to the dry air. They have tissue for 
water storage and through their thick epidermis dole it out slowly since 
there is but little water to obtain from dry soil. 

The cucurbits and the oak in their foliage leaves expose a very large sur- 
face in proportion to the mass of their substance, to an atmosphere not so 
severely dry as that of the desert, while the roots are able to obtain an 
abundant supply of water from the moist soil. The cactus and the yucca 
have differentiated their parts in a very different way from the oak or the 
cucurbits, in order to adapt themselves to the peculiar conditions of the 
environment. 

When we say that certain plants have the power to adapt themselves to 
certain conditions of environment, we do not mean to say that if the cucur- 
bits were transferred to the desert they would take on the form of the cactus 
or the yucca. They could do neither. They would perish, since the change 
would be too great for their organization. Nor do we mean, that, if the 
cactus or yucca were transferred from the desert to our climate, they would 
change into forms with thin foliage leaves. They could not. The fact is 
that they are enabled to live in our climate when we give them some care, 
but they show no signs of assuming characters like those of our vegetation. 



35 2 RELATION TO ENVIRONMENT. 

What we do mean is, that where the change is not too great nor too sudden, 
some of the plants become slightly modified. This would indicate that the 
process of organization and change of form is a very slow one, and is there- 
fore a question of time — ages it may be — in which change in environment 
and adaptation in form and structure have gone on slowly hand in hand. 

690. Members of the plant body.— The different parts into 
which the plant body has become differentiated are from one 
point of view, spoken of as members. It is evident that the sim- 
plest forms of life spoken of above do not have members. It is 
only when differentiation has reached the stage in which certain 
more or less prominent parts perform certain functions for the 
plant that members are recognized. In the algae and fungi 
there is no differentiation into stem and leaf, though there is an 
approach to it in some of the higher forms. Where this simple 
plant body is flattened, as in the sea-wrack, or ulva, it is a frond. 
The Latin word for frond is thallus, and this name is applied to 
the plant body of all the lower plants, the algae and fungi. The 
algae and fungi together are sometimes called thallophytes, or 
thallus plants. The word thallus is also sometimes applied to 
the flattened body of the liverworts. In the foliose liverworts 
and mosses there is an axis with leaflike expansions. These 
are believed by some to represent true stems and leaves; by 
others to represent a flattened thallus in which the margins are 
deeply and regularly divided, or in which the expansion has only 
taken place at regular intervals. 

In the higher plants there is usually great differentiation of 
the plant body, though in many forms, as in the duckweeds, it is 
in the form of a frond. While there is a great variety in the 
form and function of the members of the plant body, they are 
all reducible to a few fundamental members. Some reduce 
these forms to three, the root, stem, leaf; while others to two, the 
root, and shoot, which is perhaps the best primary subdivision, 
and the shoot is then divided into stem and leaf, the leaf being 
a lateral outgrowth of the stem, and can be indicated by the fol- 
lowing diagram: 



ORGANIZATION PLANT MEMBERS. 



353 



Plant body. 



Shoot, 
Root. 



Stem. 
Leaf. 



KINDS OF SHOOTS. 

691. Since it is desirable to consider the shoot in its relation to 
environment, for convenience in discussion we may group shoots 
into four prominent kinds: (i) Foliage shoots; (2) Shoots with- 
out foliage leaves; (3) Floral shoots; (4) Winter conditions 0} 
shoots and buds. Topic (4) will be treated in Chapter XXXIX, 
section IV. 

692. (1st) Foliage shoots. — Foliage shoots are either aerial, 
when their relation is to both light and air; or they are aquatic, 
when their relation is to 

both light and water. They 
bear green leaves, and 
whether in the air or water 
we see that light is one of 
the necessary relations for 
all. Naturally there are 
several ways in which a 
shoot may display its leaves 
to the light and air or 
water. Because of the 
great variety of conditions 
on the face of the earth 
and the multitudinous 
kinds of plants, there is the 
greatest diversity presented 

in the method of meeting these conditions. There is to be con- 
sidered the problem of support to the shoot in the air ; or in 
the water. The methods for solving this problem are funda- 
mentally different in each case, because of the difference in the 
density of air and water, the latter being able to buoy up the 
plant to a great degree, particularly when the shoot is provided 
with air in its intercellular spaces or air cavities. In the solu- 




Fig. 41 



Lupinus perennis. 
shoot. 



Foliage shoot and floral 



354 RELATION TO ENVIRONMENT. 

tion of the problem in the relation of the shoot to aerial en- 
vironment, stem and leaf have in most cases cooperated ; * but 
in view of the great variety of stems and their modifications, as 
well as of leaves, it will be convenient to discuss them in separate 
chapters. 

693. (2d) Shoots without foliage leaves. — These are subter- 
ranean or aerial. Nearly all subterranean shoots have also 
aerial shoots, the latter being for the display of foliage leaves 
(foliage shoots), and also for the display of flowers (flower shoots). 
The subterranean kinds bear scale leaves, i.e., the leaves not 
having a light relation are reduced in size, being small, and they 
lack chlorophyll. Examples are found in Solomon's seal, man- 




Fig. 413a. 

Burrowing type, the mandrake, a "rhizome." 

drake (fig. 413 a), etc. Here the scale leaves are on the bud at 
the end of the underground stem from which the foliage shoot 
arises. Aerial shoots which lack foliage leaves are the dodder, 
Indian pipe-plant, beech drops, etc. These plants are sapro- 
phytes or parasites (see Chapter IX). Deriving their carbo- 
hydrate food from other living plants, or from humus, they do 
not need green leaves. The leaves have, therefore, probably 
been reduced in size to mere scales, and accompanying this 
there has been a loss of the chlorophyll. Other interesting ex- 
amples of aerial shoots without foliage leaves are the cacti where 



* It is interesting to note that in some foliage shoots the stem is entirely 
subterranean. See discussion of the bracken fern and sensitive fern in 
Chapter XXXIX. 



ORGANIZATION : PLANT MEMBERS. 355 

the stem has assumed the leaf function and the leaves have 
become reduced to mere spines. The various modifications 
which shoots have undergone accompanying a change in their 
leaf relation will be discussed under stems in Chapter XXXIX. 

694. (3d) Floral shoots.— The floral shoot is the part of the 
plant bearing the flower. As interpreted here it may consist of 
but a single flower with its stalk, as in Trillium, mandrake, etc., 
or of the clusters of flowers on special parts of the stem, termed 
flower clusters, as the catkin, raceme, spike, umbel, head, etc. In 
the floral shoot as thus interpreted there are several peculiarities 
to observe which distinguish it from the foliage shoot and adapt 
it to its life relations. 

The floral shoot in many respects is comparable to the foliage 
shoot, as seen from the following peculiarities: 

(i) It usually possesses, beside the flowers, small green leaves 
which are in fact foliage though they are very much reduced in 
size, because the function of the shoot as a foliage shoot is sub- 
ordinated to the function of the floral shoot. These small leaves 
on the floral shoot are termed bracts. 

(2) It may be (a) unbranched, when it would consist of a 
single flower, or (b) branched, when there would be several to 
many flowers in the flower cluster. 

(3) The flower bud has the same origin on the shoot as the 
leaf bud; it is either terminal or axillary, or both. 

(4) The members of the flower belong to the leaf series, i.e., 
they are leaves, but usually different in color from foliage leaves, 
because of the different life relation which they have to perform. 
Evidence of this is seen in the transition of sepals, petals, sta- 
mens, or pistils, to foliage leaves in many flowers, as in the pond 
lily, the abnormal forms of trillium, and many monstrosities in 
other flowers (see Chapter XXXIV). 

(5) The position of the members of the flower on its axis, 
though usually more crowded, in many cases follows the same 
plan as the leaves on the stem. 

The various kinds of floral shoots or flower clusters will be 
discussed in Chapter XLII, on the Floral Shoot. 



35^ RELATION TO ENVIRONMENT. 

II. Organization of Plant Tissues. 

695. A tissue is a group of cells of the same kind having a 
similar position and function. In large and bulky plants differ- 
ent kinds of tissue are necessary, not only because the work of 
the plant can be more economically performed by a division of 
labor, but also cells in the interior of the mass or at a distance 
from the source of the food could not be supplied with food and 
air unless there were specialized channels for conducting food 
and specialized tissue for support of the large plant body. In 
these two ways most of the higher plants differ from the simple 
ones. The tissues for conduction are sometimes called collec- 
tively the mestome, while tissues for mechanical support are 
called stereome. Division of labor has gone further also so that 
there are special tissues for absorption, assimilation, perception, 
reproduction, and the like. The tissues of plants are usually 
grouped into three systems: (1) The Fundamental System, 
(2) The Fibrovascular System, (3) The Epidermal System. 
Some of the principal tissues are as follows: 

1. THE FUNDAMENTAL SYSTEM. 

696. Parenchyma. — Tissue composed of thin-walled cells which in the 
normal state are living. Parenchyma forms the loose and spongy tissue in 
leaves, as well as the palisade tissue (see Chapter IV) ; the soft tissue in the 
cortex of root and stem (Fig. 414) -, as well as that of the pith, of the pith 
rays or medullary rays of the stem; and is mixed in with the other elements 
of the vascular bundle where it is spoken of as wood parenchyma and bast 
parenchyma; and it also includes the undifferentiated tissue (meristem) in 
the growing tips of roots and shoots; also the "intrafascicular" cambium 
(i.e., between the bundles, some also include the cambium within the 
bundle). 

697. Collenchyma. — This is a strengthening tissue often found in the 
cortex of certain shoots. It also is composed of living cells. The cells 
are thickened at the angles, as in the tomato and many other herbs (fig. 
414). 

698. Sclerenchyma, or stone-tissue.— This is also a strengthening tissue 
and consists of cells which do not taper at the ends and the walls are evenly 
thickened, sometimes so thick that the inside (lumen) of the cell has nearly 
disappeared. Usually such cells contain no living contents at maturity. 
Sclerenchyma is very common in the hard parts of nuts, and underneath 



ORGANIZATION: PLANT TISSUES. 



357 



the epidermis of stems and leaves of many plants, as in the underground 
stems of the bracken fern, the leaves of pines (fig. 4 I 5)> etc - 




Fig. 414- Fig. 415. 

Transverse section of portion of Margin of leaf of Pinus pinaster, transverse 

tomato stem. ep, epidermis; ch section, c, cuticularized layer of outer wall 

chlorophyll-bearing cells; co, collen- of epidermis; i, inner non-cuticularized 

chyma; cp, parenchyma. layer; c', thickened outer wall of marginal 

cell; g, i\ hypoderma of elongated scle- 
renchyma; p, chlorophyll-bearing paren- 
chyma; pr, contracted protoplasmic con- 
tents. X800. (After Sachs.) 

699. Cork. — In many cases there is a development of "cork" tissue 
underneath the epidermis. Cork tissue is developed by repeated division 
of parenchyma cells in such a way that rows of parallel cells are formed 
toward the outside. These are in distinct layers, soon lose their proto- 
plasm and die; there are no intercellular spaces and the cells are usually 
of regular shape and fit close to each other. In some plants the cell walls 
are thin (cork oak), while in 
others they are thickened 
(beech). The tissue giving 
rise to cork is called "cork 
cambium," or phellogen, and 
may occur in other parts of 
the plant. For example, 
where plants are wounded the 
living exposed parenchyma 
cells often change to cork 
cambium and develop a pro- 
tective layer of cork. The 
walls of coik cells contain a 
substance termed suberin, 
which renders them nearly waterproof- 




Fig. 416- 
Section through a lenticel of Betula alba show- 
ing stoma at top, phellogen below producing rows 
of flattened cells, the cork. (After De Bary.) 



35§ RELATION TO ENVIRONMENT. 

700. Lenticels. — These are developed quite abundantly underneath 
stomates on the twigs of birch, cherry, beech, elder, etc. The phellogen 
underneath the stoma develops a cushion of cork which presses outward 
in the form of an elevation at the summit of which is the stoma (fig. 416). 
The lenticels can easily be seen. 

2. THE FIBROVASCULAR SYSTEM. 

701. Fibrous tissue* — This consists of thick-walled cells, usually with- 
out living contents which are elongated and taper at the ends so that the 
cells, or fibers, overlap. It is common as one of the elements of the vas- 
cular bundles, as wood fibers and bast fibers. 

702. Vascular tissue, or tracheary tissue. — This consists of the vessels or 
ducts, and tracheides, which are so characteristic of the vascular bundle 
(see Chapter V) and forms a conducting tissue for the flow of water. The 
vascular tissue contains spiral, annular, pitted, and scalariform vessels and 
tracheides according to the marking on the walls (figs. 58, 59). These are 
all without protoplasmic contents when mature. There are also thin- 
walled living cejls intermingled called wood parenchyma. In the conifers 
(pines, etc.) the tracheary tissue is devoid of true vessels except a few spiral 
vessels in the young stage, while it is characterized by tracheides with pecu- 
liar markings. These marks on the tracheides are due to the "bordered" 
pits appearing as two concentric rings one within the other. These can be 
easily seen in a longitudinal section of wood of conifers. 

703. Sieve tissue. — This consists of elongated tubular cells connected at 
the ends, the cross walls being perforated at the ends. These are in the 
phloem part of the bundle, and serve to conduct downwards the dissolved 
substances elaborated in the leaves. 

704. Fascicular cambium. — This is the living, cell -producing tissue in 
the vascular bundle, which in the open bundle adds to the phloem on one 
side and the xylem on the other. 

3. THE EPIDERMAL SYSTEM. 

705. To the epidermal system belong the epidermis and the various out- 
growths of its cells in the form of hairs, or trichomes, as well as the guard 
cells of the stomates, and probably some of the reproductive organs. 

706. The epidermis. — The epidermis proper consists of a single layer of 
external cells originating from the outer layer of parenchyma cells at 
the growing apex of the stem or root. These cells undergo various 
modifications of form. In many cases they lose their protoplasmic 
contents. In many cases the outer wall becomes thickened, especially 



* Some fibers occur also very frequently in the Fundamental System, 
forming bundle-sheaths, or strands of mechanical tissue in the cortex. 



ORGANIZATION: PLANT TISSUES. 



359 



in plants growing in dry situations or where they are exposed to drying 
conditions. The epidermal cells generally become considerably flattened, 
and are usually covered with a more or less well developed water-proof 
cuticle, a continuous layer over the epidermis. In many plants the cuticle 
is covered with a waxy exudation in the form of a thin layer, or of rounded 
grains, or slender rods, or grains and needles in several layers. These 
waxy coverings are sometimes spoken of as "bloom" on leaves and fruit. 

707. Trichomes. — Trichome is a general term including various hair- 
like outgrowths from the epidermis, as well as scales, prickles, etc. These 
include root hairs, rhizoids, simple or branched hairs, glandular hairs, 
glandular scales, etc. Glandular hairs are found on many plants, as 
tomato, verbena, primula, etc.; glandular scales on the hop; simple-celled 
hairs on the evening primrose, cabbage, etc.; many -celled hairs on the 
primrose, pumpkin; branched hairs on the shepherd's purse, mullein, etc., 
stellate hairs on some oak leaves. 

For stomates see Chapter IV. 



4. ORIGIN OF THE TISSUES. 

708. Meristem tissue. — The various tissues consisting of cells of dissimi- 
lar form are derived from young growing tissue known as meristem. Meri- 
stem tissue consists of cells nearly alike in form, with thin cell walls and 
rich in protoplasm. It is situated at the growing regions of the plants. 
In the higher plants these re- 
gions in general are three in 
number, the stem and root 
apex, and the cambium cyl- 
inder beneath the cortex. 
Tissues produced from the 
stem and root apex are called 
primary, those from the cam- 
bium secondary. In most 
cases the main bulk of the 
plant is secondary tissue, 
while in the corn plant it is all 
primary. 

709. Origin of stem tissues. 
— Just back of the 
meristem in 

section of a growing point it can be seen that the cells are undergoing a 
change in form, and here are organized three formative regions. The 
outer layer of cells is called dermatogen (skin producer), because later it 
becomes the epidermis. The central group of elongating cells is the plerome 
(to fill). This later develops the central cylinder, or stele, as it is called 




apical dermatogen; p, 
\. , (After De Bar v.) 

longitudinal 



P P 

Fig. 417. 
Section through growing point of stem, d, 



plerome; periblem between. 



360 



RELATION TO ENVIRONMENT. 



(fig. 417). Surrounding the plerome and filling the space between it and 
the dermatogen is the third formative tissue called the periblem, which later 
forms the cortex (bark or rind), and consists of parenchyma, collenchyma, 
sclerenchyma, or cork, etc., as the case may be. It should be understood 
that all these different forms and kinds of cells have been derived from 
meristem by gradual change. In the mature stems, therefore, there are 
three distinct regions, the central cylinder or stele, the cortex, and the 
epidermis. 

710. Central cylinder or stele. — As the central cylinder is organized from 
the plerome it becomes differentiated into the vascular bundles, the pith, 
the pith rays (medullary rays) which radiate from the pith in the center 
between the bundles out to the cortex, and the pericycle, a layer of cells 
lying between the central cylinder and the cortex. The bundles then are 
farther organized into the xylem and phloem portions with their different 
elements, and the fascicular cambium (meristem) separating the xylem 
and phloem, as described in Chapter V. Such a bundle, where the xylem 
and phloem portions are separated by the cambium is called an open bun- 




Fig. 418. 
Concentric bundle from stem of Polypodium vulgare. Xylem in the center, 
surrounded by phloem, and this by the endodermis. (From the author's Biology 
of Ferns.) 



die (as in fig. 58). Where the phloem and xylem lie side by side in the same 
radius the bundle is a collateral one. Dicotyledons and conifers are char- 
acterized by open collateral bundles. This is why trees and many other 



ORGANIZATION: PLANT TISSUES. 



361 



perennial plants continue to grow in diameter each year. The cambium 
in the open bundle forms new tissue each spring and summer, thus adding 
to the phloem on the outside and the xylem on the inside. In the spring 
and early summer the large vessels in the xylem predominate, while in 
late summer wood fibers and small vessels predominate and this part of 
the wood is firmer. Since the vascular bundles in the stem form a circle in 
the cylinder, this difference in the size of the spring and late summer wood 
produces the "annual" rings, so evident in the cross-section of a tree trunk. 
Branches originate at the surface involving epidermis, cortex, and the 
bundles. 

In monocotyledonous plants (corn, palm, etc.) the bundles are not regu- 
larly arranged to form a hollow cylinder, but are irregularly situated through 
the stele. There is no meristem, or cambium, left between the xylem and 
phloem portions of the bundle and the bundle is thus closed (as in fig. 60), 
since it all passes over into permanent tissue. In most monocotyledons 
there is, therefore, practically no annual increase in diameter of the stem. 

711. Ferns. — In the ferns and most of the Pteridophytes an apical meri- 
stem tissue is wanting, its. place being taken 
by a single apical cell from the several 
sides of which cells are successively cut 
off, though Isoetes and many species of 
Lycopodium have an apical meristem 
group. In most of the Pteridophytes also 
the bundles are concentric instead of col- 
lateral. Fig. 418 represents one of the 
bundles from the stem of the polypody 
fern. The xylem is in the center, this 
surrounded by the phloem, the phloem by 
the phloem sheath, and this in turn by 
the endodermis, giving a concentric ar- 
rangement of the component tissues. A cross-section of the stem (fig. 
419) shows two large areas of sclerenchyma, which gives the chief mechan- 
ical support, the bundles being comparatively weak. 

712. Origin of root tissues. — A similar apical meristem exists in roots, 
but there is in addition a fourth region of formative tissue in front of the 
meristem called calyptrogen (fig. 420). This gives rise to the "root cap" 
which serves to protect the meristem. The vascular cylinder in roots is 
very different from that of the stem. There is a solid central cylinder in 
which the groups of xylem radiate from the center and groups of phloem 
alternate with them but do not extend so near the center (fig. 421). As the 
root ages, changes take place which obscure this arrangement more or 
less. Branches of the roots arise from the central cylinder. In fern 
roots the apical meristem is replaced by a single four-sided (tetrahedral) 




Fig. 419. 
Section of stem (rhizome) of 
Pteris aquilina. sc, thick-walled 
sclerenchyma; a, thin - walled 
sclerenchyma ; par, parenchyma. 



362 



RELATION TO ENVIRONMENT. 



apical cell, the root cap being cut off by successive divisions of the outer 
face, while the primary root tissues are derived from the three lateral 
faces. 




Fig. 420. 

Median longitudinal section of the 
apex of a root of the barley, Hordeum 
vulgare. k, calyptrogen; d, dermat- 
ogen; c, its thickened wall; pr, peri- 
blem; pi, plerome; en, endodermis; 
*, intercellular air-space in process of 
formation; a, cell row destined to form 
a vessel; r, exfoliated cells of the root 
cap. (After Strasburger.) 



421. 



Cross-section of fibrovasculav bundle 
in adventitious root of Ranunculus re- 
pens, w, pericycle; g, four radial plates 
of xylem; alternating with them are 
groups of phloem. This is a radial 
bundle. (After De Bary.) 



Function of the root cap. — The root cap serves an important function in 
protecting the delicate meristem or cambium at the tip of the root. These 
cells are, of course, very thin-walled, and while there is not so much danger 
that they would be injured from dryness, since the soil is usually moist 
enough to prevent evaporation, they would be liable to injury from friction 
with the rough particles of soil. No similar cap is developed on the end 
of the stem, but the meristem here is protected by the overlapping bud- 
scales. One of the most striking illustrations of a root cap may be seen in 
the case of the Pandanus, or screw-pine, often grown in conservatories (see 
fig. 447). On the prop roots which have not yet reached the ground the 
root caps can readily be seen, since they are so large that they fit over the 
end of the root like a thimble on the finger. 



ORGANIZA TION : PLANT TISSUES. 



363 



713. Descriptive Classification of Tissues. 
Epidermis. 



Epidermal 
System. . 



Fibrovascular 
System 



Fundamental 
System. . . . 



Trichomes. 



Simple hairs. 

Many-celled hairs. 

Branched hairs, often stellate. 

Clustered, tufted hairs. 

Glandular hairs. 

Root hairs. 

Prickles. 



Guard-cells of stomates. 

Spiral vessels. 



Pitted vessels 

IScalariform vessels^ 
Annular vessels. 
Tracheides. 
Wood fibers. 
Wood parenchyma. 
Cambium (fascicular). 



Phloem (bast). 



Sieve -tubes. 
Bast fibers. 
Companion cells. 
Bast parenchyma. 
Cork. 



Stem and root. 



Cortex. . . • 



Pith- 



Pith. 



Collenchyma. 
Parenchyma. 
Fibers. 

Milk tissue. 

Parenchyma. 

Intra fascicular cambium. 

( Parenchyma. 
I Sclerenchyma. 



Bundle-sheath. 
Endodermis. 



\ Palisade tissue. 

< Spongy parenchyma. 



Leaves. . . 
. Reproductive Organs (mainly fundamental). 



364 RELATION TO ENVIRONMENT, 

714. Physiological Classification of Tissues. 

Formative Tissue. 

Thin-walled cells composing the meristem, capable of division and from 
which other tissues are formed. 
Protective Tissue. 

Tegumentary System. — Epidermis, periderm, bark protecting the plant 
from external contact. 

Mechanical System. — Bast tissue, bast-like tissue, collenchyma, scler- 
enchyma, afford protection against harmful bending, pulling, etc. 
Nutritive Tissues. 

Absorptive System. — Root hairs and cells, rhizoids, aerial root tissue, 
absorptive leaf glands, absorptive organs in seeds, haustoria of para- 
sites, etc. 

Assimilatory System. — Assimilating cells in leaf and stem. 

Conductive System. — Sieve tissue, tracheary tissue, milk tissue, conduct- 
ing parenchyma, etc. 

Food-storing System. — Water reservoir, water tissue, slime tissue, fleshy 
roots and stems, endosperm and cotyledons, etc. 

Aerating System. — Air spaces and tubes, special air tissue, air-seeking 
roots, stomates, lenticels, etc. 

Secretory and Excretory System. — Water glands, digestive glands, resin 
glands, nectaries, tannin, pitch and oil receptacles, etc. 
Apparatus and Tissues for Special Duties. 

Holdfasts. 

Tissues of movement, parachute hairs, floating tissue, hygroscopic tis- 
sue, living tissue. 

For perceiving stimuli. 

For conducting stimuli, etc. 



CHAPTER XXXIX. 

THE DIFFERENT TYPES OF STEMS. WINTER 
SHOOTS AND BUDS. 

I. Erect Stems. 

715. Columnar type. — The columnar type of stem may be 
simple or branched. When branching occurs the branches are 
usually small and in general subordinate to the main axis. The 
sunflower (Helianthus annuus) is an example. The foliage part 
is mainly simple. The main axis remains unbranched during 
the larger part of the growth period. The principal flowerhead 
terminates the stem. Short branches bearing small heads then 
arise in the axils of a few of the upper leaves. In dry, poor soil, 
or where other conditions are unfavorable, there may be only 
the single terminal flowerhead, when the stem is unbranched. 
The mullein is another columnar stem. The foliage part is 
rarely branched, though branches sometimes occur where the 
main axis has become injured or broken. The flower stem is 
terminal. The corn plant and the Easter lily are good illustra- 
tions also of the columnar stem. 

Among trees the Lombardy poplar (Populus fastigiata) is an 
excellent example of the columnar type. Though this is pro- 
fusely branched, the branches are quite slender and small in 
contrast with the main axis, unless by some injury or other cause 
two large axes may be developed. As the technical name indi- 
cates, the branching is fastigiate, i.e., the branches are crowded 
close together and closely surround the central axis. The royal 
palm and some of the tree ferns have columnar, simple stems, 

365 



366 



RELATION TO ENVIRONMENT. 



but the large, wide-spreading leaves at the top of the stem give 

the plant anything but a cylin- 
drical habit. Some cedars and 
arbor-vitae are also columnar. 

The advantages of the colum- 
nar habit of stem are three: (i) 
That the plant stands above 
other neighboring ones of equal 
foliage area and thus is enabled 
to obtain a more favorable light 
relation; (2) where large num- 
bers of plants of the same species 
are growing close together, they 
can maintain practically the 
same habit as where growing 
alone; (3) the advantage gained 
by other types in their neighbor- 
hood in less shading than if the 
type were spreading. The cyl- 
indrical type can, therefore, grow 
between other types with less 
competition for existence. 

716. The cone type.— This is 
well exampled in the larches, 
spruces, the gingko tree, some 
of the pines, cedars, and other 
gymnosperms. In the cone type, 
the main axis extends through 
the system of branches like a 
tall shaft, i.e., the trunk is excur- 
rent. The lower branches are 
wide-spreading, and the branches 
become successively shorter, 
usually uniformly, as one ascends 
the stem. The branching is of 

two types: (1) the branches are in false whorls; (2) the branches 





^KPisl^^H 




K ' ' ' B 

B 




L H 




B Jp'?- K*f$% :! *?qjft 




^m wV' v ' '^ w "*« 




i v/j^^5^ 




Wk s : Br '■■ '-* * v ^;~^aP 




|^L m ^Br^mm\ 




K JHI 




i^k | ^ 7 ^!11 




Rfffw 


w 









Fig. 422. 
Cylindrical stem of mullein. 



TYPES OF STEMS. 



367 




are distributed along the stem. To the first type belong the 
pines, Norway spruce, Douglas pruce, etc. The white pine is 
an exquisite example, and in 
young and middle-aged trees 
shows the style of branching to 
very good advantage. The 
branches are nearly horizontal, 
with a slight sigmoid graceful 
curve, while towards the top the 
branches are ascending. This 
direction of the branches is due 
to the light relation. The few 
whorls at the top are ascending 
because of the strong light from 
above. They soon become ex- 
tended in a horizontal direction 
as the main source of light is 
shifting to the side by the shad- 
ing of the top. The ascending 
direction first taken by the upper 
branches and their subsequent turning downward, while the ends 
often still have a slight ascending direction gives to the older 
branches their sigmoid curve. 

The young vernal shoots of the pines show some very interest- 
ing growth-movements. There are two growth periods: (1) the 
elongation of the shoot, and (2) the elongation of the leaves. 
The elongation of the shoot takes place first and is completed in 
about six weeks or two months' time. The direction of the 
shoot in the first period seems to be entirely influenced by geot- 
ropism. It grows directly upward and stands up as a very 
conspicuous object in strong contrast with the dark green foliage 
of the more or less horizontal shoots. When the second period 
of growth takes place, and the leaves elongate, the shoot bends 
downward and outward in a lateral direction. 

The rate of growth of the pines can be very easily observed 
since each whorl of branches (between the whorls of long shoots 



Fig. 423. 
Conical type of larch. 



36& DELATION TO ENVIRONMENT. 

there are short shoots bearing the needle leaves), whether on 
the main axis or on the lateral branches, marks a year; the new 
branches arising each year at the end of the shoot of the previous 
year. The rate of growth is sometimes as high as twelve to 
twenty-four inches or more per year. 

The spruces form a more perfect cone than the pines. The 
long branches are mostly in whorls, but often there are interme- 
diate ones, though the rate of growth per year can usually be 
easily determined. In the hemlock spruce, the branching is 
distributed. The larch has a similar mode of branching, but it 
is deciduous, shedding its leaves in the autumn, and it has a tall, 
conical form. 

It would seem that trees of the cone type possessed certain 
advantages in some latitudes or elevations over other trees „ 
(i) A conical tree, like the spruces and larches and the pines, 
and hemlocks also, before they get very old, meets with less injury 
during high winds than trees of an oval or spreading type. The 
slender top of the tree where the force of the wind is greatest 
presents a small area to the wind, while the trunk and short 
slender branches yield without breaking. Perhaps this is 
one reason why trees of this type exist in more northern latitudes 
and at higher elevations in mountainous regions, and why the 
spruce type reaches a higher latitude and altitude even than the 
pines. (2) The form of the tree is such as to admit light to a 
large foliage area, even where the trees are growing near each 
other. The evergreen foliage, persistent for several years, on 
the wide-spreading lower branches, probably affords some pro- 
tection to the trees since this cover would aid in maintaining a 
more equable temperature in the forest cover than if the trees 
were bare during the winter. (3) There is less danger of injury 
from the weight of snow since the greater load of snow would lie 
on the lower branches. The form of the branches also, espe- 
cially in the spruces, permits them to bend downward without 
injury, and if necessary unload the snow if the load becomes too 
heavy. 

717. The oval type. — This type is illustrated by the oak, chest- 



TYPES OF STEMS. 3 6 9 

nut, apple, etc. The trees are usually deciduous, i.e., cast their 
leaves with the approach of winter. The main axis is some- 
times maintained, but more often disappears (trunk is deliques- 
cent), because of the large branches which maintain an ascending 
direction, and thus lessen the importance of the central axis 
which is so marked in the cone type. Trees of this type, and in 
fact all deciduous trees, exhibit their character or habit to better 
advantage during the winter season when they are bare. Trees 
of this type are not so well adapted to conditions in the higher 
altitudes and latitudes as the cone type, for the reason given in 
the discussion of that type. The deciduous habit of the oaks, 
etc., enables them to withstand heavy winds far better than if 
they retained their foliage through the winter, even were the 
foliage of the needle kind and adapted to endure cold. 

718. The deliquescent type. — The elm is a good illustration 
of this type. The main axes and the branches fork by a false 
dichotomy, so that a trunk is not developed except in the forest. 
The branches rise at a narrow angle, and high above diverge 
in the form of an arch. The chief foliage development is lofty 
and spreading. 

Trees possess several advantages over vegetation less lofty. 
They may start their growth later, but in the end they outgrow 
the other kinds, shade the ground and drive out the sun-loving 
kinds. 

II. Creeping, Climbing, and Floating Stems. 

719. Prostrate type. — This type is illustrated by creeping or 
procumbent stems, as the strawberry, certain roses, of which 
a good type is one of the Japanese roses (Rosa wichuriana), 
which creeps very close to the ground, some of the raspberries, 
the curcubits like the squash, pumpkin, melons, etc. These 
often cover extensive areas by branching and reaching out radi- 
ally on the ground or climbing over low objects. The cucurbits 
should perhaps be classed with the climbers, since they are capa- 
ble of climbing where there are objects for support, but they 
are prostrate when grown in the field or where there are no ob- 



37o 



RELATION TO ENVIRONMENT. 



jects high enough to climb upon. In the prostrate type, there 
is economy in stem building. The plants depend on the ground 
for support, and it is not necessary to build strong, woody trunks 
for the display of the foliage which would be necessary in the 
case of an erect plant with a foliage area as great as some of the 







Fig. 424- 
Prostrate type of the water fern (marsilia). 

prostrate stems. This gain is offset, at least to a great extent, 
by the loss in ability to display a great amount of foliage, which 
can be done only on the upper side of the stem. 

Other advantages gained by the prostrate stems are protec- 
tion from wind, from cold in the more rigorous climates, and 
some propagate themselves by taking root here and there, as in 
certain roses, the strawberry plant, etc. Some plants have 
erect stems, and then send out runners below which take root 
and aid the plant in spreading and multiplying its numbers. 

720. The decumbent type. — In this type the stem is first erect, 
but later bends down in the form of an arch, and strikes root 
where the tip touches the ground. Some of the raspberries 
and blackberries are of this type. 



TYPES OF STEMS. 37 1 

721. The climbing type. — The grapes, clematis, some roses, 
the ivies, trumpet creeper, the climbing bittersweet, etc., are 
climbing stems. Like the prostrate type, the climbers economize 
in the material for stem building. They climb over shrubs, 
up the trunks of trees and often reach to a great height and 
acquire the power of displaying a great amount of foliage by 
sending branches out on the limbs of the trees, sometimes devel- 
oping an amount of foliage sufficient to cover and nearly smother 
the foliage of large trees; while the main stem of the vine may 
be not over two inches in diameter and the trunk of the supporting 
tree may be three feet in diameter. 

722. Floating stems. — These are necessarily found in aquatic 
plants. The stems may be ascending or horizontal. The 
stems are usually not very large, nor very strong, since the water 
bears them up. The plants may grow in shallow water, or in 
water 10-12 feet or more deep, but the leaves are usually formed 
at or near the surface of the water in order to bring them near 
the light. Various species of Potamogeton, Myriophyldum, and 
other plants common along the shores of lakes, in ponds, slug- 
gish streams, etc., are examples. Among the algae are exam- 
ples like Chara, Nitella, etc., in fresh water; Sargassum, Macro- 
cystis, etc., in the ocean. In these plants, however, the plant 
body is a thallus, which is divided into stem-like (caulidiitm) and 
leaf-like (phyllidium) structures. 

723. The burrowing type, or rhizomes. — These are horizon- 
tal, subterranean stems. The bracken fern, sensitive fern, the 
mandrake (see fig. 413a), Solomon's seal, Trillium, Dentaria, 
and the like, are examples. The subterranean habit affords 
them protection from the cold, the wind, and from injury by 
certain animals. Many of these stems act as reservoirs for the 
storage of food material to be used in the rapid growth of the 
short-lived aerial shoot. In the ferns mentioned, the subterra- 
nean is the only shoot, and this bears scale leaves which are 
devoid of chlorophyll, and foliage leaves which are larger, and 
the only member of the plant body which is aerial. The foliage 
leaf has assumed the function of the aerial shoot. The latter is 



372 



RELATION TO ENVIRONMENT. 



not necessary since flowers are not. formed. The mandrake . 
Solomon's seal, Trillium, etc., have scale leaves on the fleshy 
underground stems, while foliage leaves are formed on the aerial 
stems, the latter also bearing the flowers. Some of the advan- 
tages of the rhizomes are protection from injury, food storage 
for the rapid development of the aerial shoot, and propagation. 

Many of the grasses have subterranean stems which ramify 
for great distances and form a dense turf. For the display of 
foliage and for flower and seed production, aerial shoots are 
developed from these lateral upright branches. 

III. Specialized Shoots and Shoots for Storage of 

Food.* 

724. The bulb.— The bulb is in the form of a bud, but the 
scale leaves are large, thick, and fleshy, and contain stored in 

them food products manu- 
factured in the green aerial 
leaves and transported to the 
underground bases of the 
leaves. Or when the bulb is 
aerial in its formation, it is 
developed as a short branch of 
the aerial stem from which 
the reserve food material is 
transported. Examples are 
found in many lilies, as Easter 
lily, Chinese lilies, onion, tulip, 
etc. The thick scale leaves are 
closely overlapped and surround the short stem within (also 
called a tunicated stem). In many lilies there is a sufficient 




Fig. 425- 
Bulb of hyacinth. 



* Besides these specialized shoots for the storage of food, food-substances 
are stored in ordinary shoots. For example, in the trunks of many trees 
starch is stored. With the approach of cold weather the starch is con- 
verted into oil, in the spring it is converted into starch again, and later as the 
buds begin to grow the starch is converted into glucose to be used for food 
In many other trees, on the other hand, the starch changes to sugar on the 
approach of winter. 






TYPES OF STEMS. 



373 



amount of food to supply the aerial stem for the development 
of flower and seed. There are roots, however, from the bulb 
and these acquire water for the aerial shoot, and when planted 
in soil additional food is obtained by them. 

725. Corm. — A corm is a thick, short, fleshy, underground 
stem. A good example 
is found in the jack-in-the- 
pulpit (Arisaema). 

726. Tubers. — These 
are thickened portions of 
the subterranean stems. 
The most generally known 
example is the potato 
tuber ("Irish" potato, not 
the sweet potato, which 
is a root). The "eyes" of 
the potato are buds on the 
stem from which the aerial 
shoots arise when the po- 
tato sprouts. The potato 
tuber is largely composed 
of starch which is used for 
food by the young sprouts. 

726a. Phylloclades. — 
These are trees, shrubs, or 
herbs in which the leaves are reduced to mere bracts and stems, 
are not only green and function as leaves, but some or all of the 
branches are flattened and resemble leaves in form as in Phyl- 
lanthus, Ruscus, Semele, Asparagus, etc. The flowers are borne 
directly on these flattened axes. The prickly pear cactus 
(Opuntia) is also a phylloclade. Examples of phylloclades are 
often to be found in greenhouses. 

727. Undifferentiated stems are found in such plants as the 
duckweed, or duckmeat (Lemna, Wolffia, etc. See Chapter III). 




Fig. 426. 
Corm of Jack-in-the-pulpit. 



374 



RELATION TO ENVIRONMENT. 



IV. Annual Growth and Winter Protec- 
tion of Shoots and Buds.* 

728. Winter conditions.! — While herbs are 
subjected only to the damp warm atmosphere 
of summer, woody plants are also exposed dur- 
ing the cold dry winter, and must protect them- 
selves against such conditions. The air is dryer 
in winter than in summer; while at the same 
time root absorption is much retarded by the 
cold soil. Then, too, the osmotic activity of 
the dormant twig-cells being much reduced, the 
water-raising forces are at a minimum. It is 
easy to see, therefore, that a tree in winter is prac- 
tically under desert conditions. Moreover, it has 
been found by various investigators, contrary to 
the general belief, that cold in freezing is only indi- 
rectly the cause of death. The real cause is the 
abstraction of water from the cell by the ice crys- 
tals forming in the intercellular spaces. Death 
ensues because the water content is reduced below 
the danger-point for that particular cell. It was 
formerly thought that on freezing, the cells in the 
tissue were ruptured. This is not so. Ice almost 
never forms within the cell, but in the spaces 
between. Freezing then is really a drying proc- 
ess, and dryness, not cold, causes death in winter. 
To protect themselves in winter, trees provide 
various waterproof coverings for the exposed sur- 
faces and reduce the activity of the protoplasm 
so that it will be less easily harmed by the loss of 
water abstracted by the freezing process. 

729. Protection of the twig. — Woody plants 
Fig. 427- protect the living cells within the twigs by the 

of horee-chfstS production of a dull or rough corky bark, or by a 

showing buds and 

leaf-scars. (A twig 

with a terminal bud * This topic was prepared by Dr. K. M. Wiegand. 

should have been se- , .. . r _, , . . _ , •«,.,, ^ 

lected for this figure.) \ See discussion of Tropophytes in Chapter XL VI, 



Two- 



TYPES OF STEMS. 375 

thick glossy epidermis over the entire surface. At intervals 
occur small whitish specks called lenticels, which here perform 
nearly the same function as do stomates in the leaf. 

730. Bark of trunk. — A similar service is performed by the 
bark for the main trunk and branches of the tree. To admit of 
growth in diameter the old bark is constantly being thrown off 
in strips, flakes, etc., and replaced by a new but larger cylinder 
of young bark. The external appearance thus produced enables 
experienced persons to recognize many kinds of trees by the 
trunk alone. 

731. Leaf-scars and bundle-scars. — The presence of foliage 
leaves during the winter would greatly increase the transpiring 
surface without being of use to the plant; hence they are usually 
thrown off on the approach of winter. The scars left by the 
fallen leaves are termed leaf-scars. The small dots on the leaf- 
scars left by the vascular bundles which extended through the 
petiole into the twig are termed bundle-scars. Sometimes 
stipule-scars are left on each side of the leaf-scar by the fallen 
stipules. 

732. Nodes and internodes. — The region upon a stem where 
a leaf is borne is termed a node. The space between two nodes 
is an internode. 

733. Phyllotaxy. — Investigation of a horse-chestnut or willow twig will 
show that the leaf-scars occupy definite positions which are constant for 
each plant but different for the two species. The arrangement of the 
leaves on the stem in any plant is termed phyllotaxy. In the horse- 
chestnut we find two scars placed at the same node, but on opposite sides 
of the stem. Somewhat higher up we find two more similarly placed, but 
in a position perpendicular to that of the first pair. Such phyllotaxy is 
termed opposite. If in any plant several leaves occur at a node, the phyl- 
lotaxy is whorled. If but one at each node, as in the willow, the phyllotaxy 
is alternate. The opposite and alternate types are very commonly met 
with. Closer observation will show that in the willow, if a line be drawn 
connecting the successive leaf-scars, it will pass spirally up the twig until 
at length a scar is reached directly over the one taken as a starting-point. 
Such spiral arrangement always accompanies alternate phyllotaxy. The 
section of the spiral thus delineated is termed a cycle. We express the 
nature of the cycle by the fractions |, -J, f, f, T 5 a , etc., in which the 



376 



RELATION TO ENVIRONMENT. 



Fig. 428. Fig. 429. 

Fig. 428. — Shoot of butternut 
showing leaf -scars, axillary buds, 
and adventitious buds (buds com- 
ing from above the axils). 

Fig. 429. — Shoot and bud of 
white oak. 



numerator denotes the number of turns 
around the stem in each cycle, and the 
denominator the number of leaf-scars in 
the same distance. In a general way we 
find in plants only such arrangements as 
are represented by the fractions given 
above. These fractions show the curious 
condition that the numerator and de- 
nominator of each is equal to the sum 
of the numerator or denominator of the 
two preceding fractions. Much specula- 
tion has been indulged in regarding the 
significance of these definite laws of leaf- 
arrangement. In part they may be due 
to the desire that each leaf receive the 
maximum amount of light. Only certain 
definite geometrical conditions wall insure 
this. More likely it is due to the economy 
of space alotted to the leaf-fundaments 
in the bud. Here, again, geometiical 
laws govern this economy. The phyllo- 
taxy is nearly constant for a given species. 

734. Buds. — The growing point 
of the stem or branch together with 
its leaf or flower fundaments and 
protective structures is termed a 
bud. Winter buds on woody plants 
are terminal when inclosing the 
growing point of the main axis of the 
twig; lateral when the growing point 
is that of a branch of the main 
axis. Lateral buds are always axil- 
lary, i.e., situated on the upper angle 
between a leaf and the main axis. 

735. Buds occupying special po- 
sitions. — Several species of trees 
and shrubs produce more than one 
bud in each leaf-axil. The addi- 
tional ones are termed accessory or 
supernumerary buds. These may 



TYPES OF STEMS. UJ 

be lateral to one another or they may be superposed as in the wal- 
nut or butternut. In such cases some of the buds usually contain 
simply floral shoots and are termed flower-buds. In some species 
buds are frequently produced on the side of the branches and 
trunk at some distance from the leaf-axils, and entirely without 
regard for the latter; or more rarely may occur upon the root. 
Such buds are termed adventitious, and are the source of the 
feathery branchlets upon the trunks of the American elm. 

736. Branching follows the phyllotaxy. — Since the lateral or 
branch-producing buds are always located in the axil of a leaf, 
the branches necessarily follow the same arrangement upon the 
main axis as do the leaves. Since, however, many of the axil- 
lary buds fail to develop, this arrangement may be more or less 
obscured. 

737. Coverings of winter-buds. — These are of two sorts, hair 
and cork, or scales. Buds protected simply by dense hair or 
sunk in the cork of the twig are termed naked buds, and are 
comparatively rare. Most species protect their buds by the 
addition of an imbricated covering of closely appressed scales, 
the whole frequently being rendered still more water-proof by 
the excretion of resin between the scales or over the whole sur- 
face. The scales when studied carefully are found to be much 
reduced leaves or parts of leaves. In some cases they represent 
a modified whole leaf, when they are said to be laminar, or a 
leaf -petiole, when they are petiolar, or stipular, when they are 
much-specialized stipules of a leaf which itself is usually absent. 
The latter type is much the less common. The form of the bud, 
the nature and form of the scales, when combined with characters 
furnished by the leaf- and bundle-scars, enable one to recog- 
nize and classify the winter twigs of the various woody species. 

738. Phyllotaxy of the bud-scales. — Since the bud-scales are 
leaves, they follow a definite phyllotaxy. This may or may not 
be the same as that of the foliage leaves. Twigs with opposite 
leaves have opposite bud-scales, or if with alternate leaves, then 
alternate bud-scales, but the fractions vary. If the scales are 
stipular, then there are of course two at each node. 



373 



RELATION TO ENVIRONMENT. 



739. Function of the bud-coverings. — It is popularly be- 
lieved that the scales and hairy coverings serve to keep the bud 
warm. Research, however, shows this 
to be almost entirely erroneous, and 
that the thin bud coverings are en- 
tirely inadequate to keep out the cold 
of winter. They cannot keep the 
bud even a degree or two warmer than 
the outside air, except when the 
changes are very rapid. Experiment 
also shows that the modifying effect 
of the covering when the bud thaws 
out is so slight as to be almost neg- 
ligible. Indeed, a thermometer bulb 
covered with scales taken from a 
horse-chestnut bud warmed up more 
rapidly than a naked one when ex- 
posed to sunshine. The wool in the 
horse-chestnut bud is not for the pur- 
pose of keeping it warm, but to pro- 
tect the young shoot from too great 
transpiration after the bud opens the 
following spring. Research has also 
Bud of European elm in sec- shown that such tempering of the 

tion, snowing overlapping 01 ± o 

scales - heat conditions is not especially bene- 

ficial to the plant, as was once thought. Neither can we find the 
main function in the prevention of water from entering the bud. 
This might be accomplished in much simpler ways, even if we 
could demonstrate the desirability of keeping the water out at all. 
The true functions of the bud-scales are two in number: 
Firstly, the prevention of too great loss of water from the young 
and delicate parts within; and secondly, the protection of these 
same parts from mechanical injury. Without some such pro- 
tection the delicate young structures would be beaten off by the 
wind, or become the food for hungry birds during the long win- 
ter months, 




Fig. 430. 



TYPES OF STEMS. 



379 



740. Opening of the buds. — When the young shoot begins to 
grow in the spring, the bud-scales are forced apart or open of 
their own accord. During the young condition the shoot is very 
soft and brittle, and also possesses a very thin, little cutinized 
epidermis. In this condition it is especially liable to mechanical 




Fig. 431. 
Opening buds of hickory. 



injury and to injury from drying out. We find, therefore, a 
tendency for the inner bud-scales to elongate during vernation, 
thus forming a tube around the delicate tissue much like the 
opening out of a telescope. The young leaves and internodes 



380 RELATION TO ENVIRONMENT, 

themselves are often provided with a woody or hairy covering 
to retard transpiration. When the epidermis becomes more 
efficient the hairy covering often falls away. 

In the case of naked buds protection is afforded in other ways : 
by the protection of hairy covering, by physiological adaptation of 
the tissue, or in many cases by the late appearance of the shoot 
in spring after the very dry April and May winds have ceased. 

741. Bud-scars, and how to tell the age of the plant. — In gen- 
eral the bud-scales when they fall away in the spring leave scars 
termed scale-scars, and the whole aggregate of scale-scars makes 
up the bud-scar. The position of the buds of previous winters is, 
therefore, marked. It becomes an easy matter to determine the 
age of a branch, since all that is necessary is to follow back from 
one bud-scar to another, the portion of the stem between repre- 
senting, except in rare cases, one year's growth. 

A woody plant grows in height only by the formation of new 
sections of stem added to the apex or side of similar sections 
produced the previous season, never, as is commonly supposed, 
by the further elongation of the previous year's growth. Hence a 
branch once formed upon a tree is fixed as regards its distance 
from the ground. The apparent rise of the branches away from 
the ground in forest trees is an illusion caused by the dying away 
of the lower branches. 

742. Definite and indefinite growth. — With the opening of 
the buds in spring, growth begins. In some cases, when all the 
members for the season were formed, but still minute, within the 
bud, such growth consists solely in the expansion of parts already 
formed; in others only a few members are thus present to ex- 
pand, while new ones are produced by the growing point as the 
season progresses. In most cases growth is completed by the 
middle of July, soon after which buds are formed for next year's 
growth. Such a method of growth is termed definite. 

In a few woody plants, as, for example, sumach, locust, and 
raspberry, growth continues until late in the autumn. In such 
cases the most recently formed nodes and internodes are unable 
to become sufficiently " hardened" before winter sets in 7 and 



TYPES OF STEMS. 



381 



are killed back more or less. Next season's shoot is a branch 
from some axillary bud. Such growth is termed indefinite. 

743. Structure of woody stems. — If we make a cross-section of a woody 
twig three general regions are presented to view. On the outside is the 
rather soft,often greenish " bark," 
so called, made up of sieve - 
tubes, ordinnry parenchyma 
cells, and in many cases long 
fibrous cells composing the "fi- 
brous bark." From a growing 
layer in this region, termed the 
phellogen, the true corky bark 
of the older trunk is formed. 

Next within the bark we find 
the so-called "woody" portion 
of the twig. This is strong and 
resistant to both breaking and 
cutting. The microscope shows 
it to be composed of the ordi- 
nary already known woody ele- 
ments,* wood-fibers, for 
strengthening purposes, pitted 
and spiral vessels as conducting 
tissue ; and intermixed with these 
some living parenchyma cells. 
A cross-section of the stem also 
shows narrow radial lines through 
the wood. These are pith-rays, 
composed of vertical plates of 
living parenchyma cells. These 
cells, unlike the others in the 
wood, are elongated radially, 
not vertically. The height of the 
pith-rays as well as their thick- 
ness varies with the species studied. In the older trunk only the outer por- 
tion, a few inches in thickness, remains light-colored and fresh, and is called 
sap-wood. The inner wood is usually darker and harder, and is termed 
heart-wood. Living parenchyma cells, in general, are present only in the 
sap-wood, and in this almost solely the ascent of sap occurs. Dyestuffs 
and other substances are frequently deposited in the walls of the heart-wood. 

The third region occupying the center of the twig is the pith. This 

* Chapter V, and Organization of Tissues in Chapter XXXVIII. 




Fig. 432. 
Three-year-old twig of the American ash, 
with sections of each year's growth showing 
annual rings. 



3^2 RELATION TO ENVIRONMENT. 

is composed ordinarily of angular, little elongated, parenchyma cells, 
when mature mostly without cell-contents and filled with air. The pith 
region in different trees is quite diversified. It may be hollow, chambered, 
contain scattered thick-walled cells, have woody partitions, or rarely be 
entirely thick-walled. 

The nature of the woody ring is rather perplexing at first; but its origin 
is simple. We may conceive that it has developed from a stem-type like the 
sunflower, in which the bundles, though separate, are connected by a con- 
tinuous cambium ring. In the woody twigs the numerous bundles are 
closely packed together, and only separated by the primary pith-rays ex- 
tending from the pith to the cortex. Other secondary pith-rays are pro- 
duced within each bundle, but they usually extend only part way from 
the cortex to the pith. The wood represents the xylem of the bundle, 
and the sieve-tubes of the bark, the phloem. 

744. Growth in thickness. — Although the year's growth does not in- 
crease in length after the first season has passed, it does increase in diam- 
eter very much. From the size of an ordinary little twig it may at length 
become a large tree trunk several feet in thickness. Only a portion of the 
first year's growth is produced by the growing point. All the rest is a 
product of the cambium, a cylinder of wood being added to the exterior 
of the old wood each season. The cambium, here, as in the sunflower, lies 
between the phloem and the xylem, forming a cylinder entirely around 
the stem. In spring, when active, it becomes soft and delicate, thus en- 
abling one to easily strip off the bark from some trees, such as willow, etc., 
at that season. 

745. Annual rings in woody stems. — The wood produced by the cam- 
bium each season is not homogeneous throughout, but is usually much 
denser toward the outer part of the yearly cylinder, wood-fibers here pre- 
dominating. In the inner portion vessels predominate, giving a much 
more porous effect. The transition from one year's growth to another 
is very abrupt, giving rise to the appearance of rings in cross-section. Since 
ordinarily in temperate climates but one cylinder of wood is added each 
year, the number of rings will indicate the age of the trunk or branch. 
This is not absolutely accurate, since in some trees under certain conditions 
more than one ring may be produced in a summer. The porous part 
of the ring is often termed "spring wood," and the denser portion "fall 
wood," but since growth from the cambium ceases in most trees by the 
middle of July, "summer wood" would be more appropriate for the latter. 
It is mainly the alternation of the cylinders of the spring and summer 
wood that gives the characteristic grain to lumber. Pith-rays play an 
important part in wood graining only in a few woods, as, for instance, in 
quartered oak. The reason for the production of porous spring wood 
and dense summer wood is still one of the unsolved problems of botany. 



CHAPTER XL. 

FOLIAGE LEAVES. 

I. General Form and Arrangement of Leaves. 

746. Influence of foliage leaves on the form of the stem. — 

The marked effect which foliage has upon the aspect of the plant 
or upon the landscape is evident to all observers. Perhaps it is 
usual to look upon the stem as having been developed for the 
display of the foliage without taking into account the possibility 
that the foliage may have a great influence upon the form or 
habit of the stem. It is very evident, however, that the foliage 
exercises a great influence on the form of the stem. For ex- 
ample, as trees increase in age and size, the development of 
branches on the interior ceases and some of those already formed 
die, since the dense foliage on the periphery of the trees cuts 
off the necessary light stimulus. The tree, therefore, possesses 
fewer branches and a more open interior. In the forest also, 
the dense foliage above makes possible the shapely, clean timber 
trunks. Note certain trees where by accident, or by design, the 
terminal foliage-bearing branches have been removed that foliage- 
bearing branches may arise in the interior of the tree system. 

Without foliage leaves the stems of green plants would develop 
a very different habit from what they do. This development 
could take place in three different directions under the influence 
of light: (i) The light stimulus would induce profuse branch- 
ing, so that there would be many small branches. (2) The stem 
would develop fewer branches, but they would be flattened. 
(3) Massive trunks with but few or no branches. In fact, all 

383 



384 RELATION TO ENVIRONMENT. 

these forms are found in certain green stems which do not bear 
leaves. An example of the first is found in asparagus with its 
numerous crowded slender branches. But such forms in our 
climate are rare, since foliage leaves are more efficient. The 
second and third forms are found among cacti, which usually 
grow in dry regions under conditions which would be fatal to 
ordinary thin foliage leaves. 

747. Relation of foliage leaves to the stem. — In the study of 
the position of the leaves on the stem we observe two important 
modes of distribution: (1) the distribution along the individual 
stem or branch which bears them, usually classed under the 
head of Phyllotaxy; (2) the distribution of the leaves with refer- 
ence to the plant as a whole. 

748. Phyllotaxy, or arrangement of leaves. — In examining buds on the 
winter shoots of woody plants, we cannot fail to be impressed with some 
peculiarities in the arrangement of these members on the stem of the plant. 

In the horse-chestnut, as we have already observed, the leaves are in 
pairs, each one of the pair standing opposite its partner, while the pair 
just below or above stand across the stem at right angles to the position of 
the former pair. In other cases (the common bed-straw) the leaves are 
in whorls, that is, several stand at the same level on the axis, distributed 
around the stem. By far the larger number of plants have their leaves 
arranged alternately. A simple example of alternate leaves is presented 
by the elm, where the leaves stand successively on alternate sides of the 
stem, so that the distance from one leaf to the next, as one would measure 
around the stem, is exactly one half the distance around the stem. This 
arrangement is one half, or the angle of divergence of one leaf from the 
next is one half. In the case of the sedges the angle of divergence is less, 
that is one third. 

By far the larger number of those plants which have the alternate arrange- 
ment have the leaves set at an angle of divergence represented by the frac- 
tion two fifths. Other angles of divergence have been discovered, and 
much stress has been laid on what is termed a law in the growth of the 
stem with reference to the position which the leaves occupy. Singularly 
by adding together the numerators and denominators of the last two fractions 
gives the next higher angle of divergence. Example: - ,- = |; - ,1= > 
and so on. There are, however, numerous exceptions to this regular 
arrangement, which have caused some to question the importance of any 
theory like that of the "spiral theory" of growth propounded by Goethe 
and others of his time. 



FOLIAGE LEAVES. 385 

749. Adaptation in leaf arrangement. — As a result, however, of one 
arrangement or another we see a beautiful adaptation of the plant parts 
to environment, or the influence which environment, especially light, has 
had on the arrangement of the leaves and branches of the plant. Access 
to light and air are of the greatest importance to green plants, and one 
cannot fail to be profoundly impressed with the workings of the natural 
laws in obedience to which the great variety of plants have worked out 
this adaptation in manifold ways. 

750. Distribution of leaves with reference to the entire plant. — In this 
case, as in the former, we recognize that it is primarily a light relation. 
As the plant becomes larger and more branched the lower and inner leaves 
disappear. The trees and shrubs have by far the larger number of leaves 
on the periphery of the branch system. A comparison of different kinds 
of trees in this respect shows, however, that there is great variation. Trees 
with dense foliage (elm, Norway maple, etc.) present numerous leaves 
on the periphery which admit but little light to the interior where leaves 
are very few or wanting. The sugar maple and red maple do not cast 
such a dense shade and there are more leaves in the interior. This is 
more marked in the silver maple, and still more so in the locust (Gledit- 
schia tricanthos). 

751. Color of foliage leaves. — The great majority of foliage leaves are 
green in color. This we have learned (Chapter VII) is due to the presence 
of a green pigment, chlorophyll, in the chloroplastids thickly scattered in 
the cells of the leaf. We have also learned that in the great majority of 
cases, the light stimulus is necessary for the production of chlorophyll 
green. There are many foliage leaves which possess other colors, as red 
(Rosa rubrifolia), purple (the purple barberry, hazel, beech, birch, etc.), 
yellow (the golden oak, elder, etc.); while many others have more or less 
deep tints of pink, red, purple, yellow, when young. All of these leaves, 
however, possess chlorophyll in addition to red, yellow, purple or other 
pigment. These other pigments are sometimes developed in great quan- 
tity in the cell-sap. They obscure the chlorophyll from view, but do not 
interfere seriously with the action of light and the function of chlorophyll, 
and perhaps in some cases serve as a screen to protect the protoplast. 

752. Autumn colors. — Foliage leaves of many trees display in the autumn 
gorgeous colors. These colors are principally shades of red or yellow, 
and sometimes purple. The autumn color is more marked in some trees 
than in others. In the red maple, the red and scarlet oak, the sourwood, 
etc., red predominates, though sometimes yellow may be present with 
the red in a single leaf. Sugar maples, poplars, hickories, etc., are prin- 
cipally yellow in autumn. The sweet gum has a rich variety of color-red, 
purple, maroon, yellow; sometimes all these colors are present on the same 
tree 



386 RELATION TO ENVIRONMENT. 

The red and purple colors are found suffused in the cell-sap of certain 
cells in the leaf much as we have found it in the cells of the red beet. The 
yellow color is chiefly due to the disappearance and degeneration of the 
chlorophyll while the leaf is in a moribund state. A similar phenomenon 
is seen in the yellowing of crops when the soil becomes too wet, or in the 
blanching of grass when covered with a board, or of celery as the earth 
is ridged up over the leaves in late summer and autumn. A number of 
different theories have been advanced to explain autumn coloring, i.e., 
the appearance of the red coloring-matter. It has been, attributed to the 
approach of cold weather, and this has likely led to the erroneous belief 
on the part of some that it is caused by frost. It very often precedes frost. 
Some have attributed it to the action of the more oblique light rays during 
autumn, and still others to the diminishing water-supply with the approach 
of cool weather. The question is one which has not met as yet with a 
satisfactory solution, and is certainly a very obscure one. It is likely 
that the low temperature or the declining activities of the leaf affect certain 
organic substances in the leaf and give rise to the red color, and it is quiU 
certain that in some years the display is more brilliant than in others. 
The color is more striking in some regions than in others and the different 
soil, as well as climate, has been supposed to have some influence. The 
North American forests are noted for the brilliant display of autumnal 
color. This is perhaps due to some extent to the great variety or number 
of species which display color. It would seem that there is some specific 
as well as individual peculiarities in certain trees. Some individuals, 
for example, exhibit brilliant colors every autumn, while others near of 
the same species are more subdued. 

It has been shown by experiment that when sunlight passes through 
red colors the temperature is slightly increased, and it has been suggested 
that this may be of protection to the living substance which has ceased 
working and is in danger of injury from cold. There does not seem to 
be much ground for this suggestion, however. It certainly could not 
protect the protoplasm of the leaf at night when the cold is more intense, 
and during the day would only aggravate matters by supplying an in- 
creased amount of heat, since extremes of heat and cold in alternation 
are more harmful to plant life than uniform cold. Especially would this 
be the case in alpine climates where the alternation of heat and cold be- 
tween day and night is extreme, and brilliancy of the colors of alpine plants 
is well known. It seems more reasonable to suppose that the red color 
acts as a screen, as the chlorophyll is disappearing, to protect from the 
injurious action of light, certain organic substances which are to be trans- 
ferred back from the leaf to the stem for winter storage. So in the case 
ot many stems in the spring or early summer when the young leaves often 
have a reddish color, it is likely that it acts as a screen to protect the living 



FOLIAGE LEAVES. 3^7 

Substance from the strong light at that season of the year until the chloro- 
phyll screen, which is weak in young leaves, becomes darker in color and 
more effective, when the red color often disappears. 

753. Function of foliage leaves. — In general the function of 
the foliage leaf as an organ of the plant is fivefold (see Chapters 
IV, VII, VIII, XI), (i) that of carbon-dioxide assimilation or 
photosynthesis, (2) that of transpiration, (3) that of the synthesis 
of other organic compounds, (4) that of respiration, and (5) that 
of assimilation proper, or the making of new living substance. 
While none of these functions are solely carried on in the leaf, 
it is the chief seat of the first three of these processes, its form, 
position, and structure being especially adapted to the purpose. 
Assimilation proper, as well as respiration, probably take place 
equally in all growing or active parts. 

754. Parts of the leaf. — All foliage leaves possess a blade or 
lamina, so called because of its expanded and thin character. 
The blade is the essential part. Many leaves, however, are 
provided with a stalk or petiole by which the blade is held out 
at a greater or lesser distance from the stem. Leaves with no 
petiole are sessile, the blade is attached by one end directly on 
the stem. In some cases the base of the blade is wrapped partly 
around the stem, or in others it extends entirely around the 
stem and is perfoliate. Besides, many leaves have short append- 
ages, termed stipules, attached usually on opposite sides of the 
petiole at its junction with the stem. In some species of magnolia 
the stipules are so large that each one envelops the entire portion 
of the bud which has not yet opened. Many leaves possess out- 
growths in the form of hairs, scales, etc. (See leaf protection.) 

755. Simple leaves. — Simple leaves are those in which the 
blade is plane along the edge, not divided. The edge may be 
entire or indented (serrate) to a slight extent as in the elm. The 
form of the simple leaf varies greatly but is usually constant 
for a given species, or it may vary in shape in the same species 
on different parts of the plant. Some of the terms applied to 
the outline of the leaf are ovate, oval, elliptical, lanceolate, 
linear, needle-like, etc., but it is idle for one to waste time on 



388 RELA TION TO ENVIRONMENT. 

matters of minute detail in form until it becomes necessary for 
those in the future who pursue taxonomic work. It is evident 
that a simple leaf, except those of minute size, possesses advantages 
over a divided leaf in the amount of surface it exposes to the 
light. But in other respects it is at a disadvantage, especially 
as it increases in size, since it casts a deeper shade and does 
not admit of such a free circulation of air. It will be found, 
however, in our study of the relation of leaves to light and air 
that the balance between the leaf and its environment is ob- 
tained in the relation of the leaves to each other. 

756. Venation of leaves. — A very prominent character of the 
leaf is its "venation. " This is indicated by the presence of numer- 
ous " veins," indicated usually by narrow depressed lines on the 
upper surface, and by more or less distinct elevated lines on the 
under surface. There are two general types: (i) In the corn, 
Smilacina, Solomon's seal, etc., the veins extend lengthwise of the 
leaf and are nearly parallel. Such leaves are said to be parallel- 
veined. It is generally, though not always, a character of mono- 
cotyledenous plants. (2) In the elm, rose, hawthorn, maple, oak, 
etc., the veins are not all parallel. The larger ones either diverge 
from the base of the blade (palmate leaf, maple), or the mid- 
vein extends through the middle line of the leaf, while other 
prominent ones branch off from this and extend, nearly parallel, 
toward the edge of the leaf (pinnate venation). The smaller 
intermediate veins which are also very distinct extend irregularly 
and branch and anastomose in such a fashion as to give the figure 
of a net with very fine meshes. These are netted-veined leaves. 
These are characteristic of most of the dicotyledenous plants. 
It is evident from what has been said of the examples cited that 
there are two types of netted-veined leaves, the palmate and pinnate. 

Note. As we have already learned in Chapter V the veins contain the 
vascular bundles of the leaf. Through them the water and food solutions 
are distributed to all parts of the leaf, and the return current of food ma- 
terial elaborated in the leaf moves back through the bast portion into the 
shoot. The veins also possess a small amount of mechanical tissue. This 
forms the framework of the leaf and aids in giving rigidity to the leaf and 



FOLIAGE LEAVES. 



389 



in holding it in the expanded position. The mechanical tissue in the 
framework alone could not support the leaf. Turgescence of the meso- 
phyll is needed in addition. 

757. Cut or lobed leaves. — In many leaves, the indentations 
on the margin are few and 
deep. Such leaves pre- 
sent several lobes the pro- 
portionate size of which 
is dependent upon the 
depth of the indentation 
or "incision." Several 
of the maples, oaks, 
birches, the poison ivy, 
thistles, the dandelion, 
etc., have lobed leaves. 
Where the indentation 
reaches to or very near 
the midrib the leaf is 
said to be cut. A study 
of various leaves will 
show all gradations from 
simple leaves with plane edges to those which are cut or divided, as 
in compound leaves, and the lobes are often variously indented. 

758. Divided, or compound leaves. — The rose, sumac, elder, 
hickory, walnut, locust, pea, clover, American creeper, etc., are 
examples of divided or compound leaves. The former are pin- 
nately compound, and the latter are palmately compound. The 
leaf of the honey-locust is twice pinnately compound or bipin- 
nate, and some are three times pinnately compound.* It is 

* Some of the different terms used to express the kinds of compound 
leaves are as follows : 

Unifoliate (for a single leaflet, as in orange and lemon where the com- 
pound leaf is greatly reduced and consists of one pinna attached to the 
petiole by a joint). Bifoliate for one with two leaflets; trifoliate for one 
with three leaflets, as in the clover; pi uri foliate for many leaflets. Odd 
pinnate for a pinnate leaf with one or more pairs of leaflets and one odd 
leaflet at the end. 




Fir. 433. 
Lobed leaves of oak forming a mosaic. 



390 



RELATION TO ENVIRONMENT. 




evident that compound leaves are only extreme forms of lobed 
or cut leaves and that the form of all bears a definite relation 
to the primary venation. There has been a reduction of meso- 
phyll and of the area of smaller venation. 

759. These forms of leaves probably have some definite sig- 
nificance. It is not quite clear why they should have developed as 

they have; though it is 
possible to explain several 
important relations of these 
forms to their environ- 
ment, (i) The reduction 
of the surface of the leaf, 
with the retention of the 
firmer portions, allows 
freer movement of the air 
and affords the leaf greater 
protection from injury dur- 
ing violent winds, just as 
the finely dissected leaves 
of some water - plants 
are less liable to injury from movement of the more dense 
medium in which they live. It is possible that here we may 
have an explanation of one of the factors involved in this 
reduction of leaf surface. (2) In trees with compound leaves, 
like the hickory, walnut, locust, ailanthus, etc., the midvein, 
and in the case of the Kentucky coffee-tree (Gymnocladus) the 
primary lateral veins also, serve in place of terminal branches 
of the stem. By the increase in the outline of the leaf and 
the reduction of its surface between the larger veins, the tree 
has attained the same leaf development that it would were the 

So leaves are palmately bifoliate, etc., pinnately bifoliate, etc. Decom- 
pound leaves are those where they are more than twice compound, as 
temately decompound in the common meadow rue (Thalictrum). 

Perfoliate leaves are seen in the bellwort (Uvularia), connate perfoliate, 
as in some of the honeysuckles where the bases of opposite leaves are joined 
together around the stem. Equitant leaves are found in the iris ? where the 
Jeaves fit over one another at the base like a sacldle ? 



Fig. 434- 
Twice compound leaf. Leaflets arranged in 
one plane, but open spaces permit free circula- 
tion of air through the large leaf. 



FOLIAGE LEAVES. 39 1 

larger veins replaced by stems bearing simple leaves. The tree 
as it is, however, has the advantage of being able to cast off for 
the winter period a layer of what otherwise would have been a 
portion of the stem system, to retain which through the winter 
would use more energy than with the present reduced stem 
system, and the stouter stem is less liable to dry out. In the 
case of herbaceous plants, in the case of plants like most of 
the ferns where the stem is on the underground rootstock (Pteris) , 
or a very short erect stem, as in the Christmas fern, the leaf 
replaces the aerial stem, and the division (or branching, as it is 
sometimes styled) of the leaf corresponds to the branching of the 
stem. This is more marked in the gigantic exotics like Cibo- 
tium regale, and in the tree ferns which have quite tall trunks, 
the massive compound leaves replace branches. In the palms 
and cycads are similar examples. Those who choose to observe 
can doubtless find many examples close at hand. (3) While 
divided leaves have probably not been evolved in response to 
the light relation, still their relation in this respect is an impor- 
tant one, since if the leaf with its present size were entire, it 
would cast too dense a shade on other leaves below. 

760. General structure of the leaf. — The general structure of the leaf 
has been already studied (see Chapters IV, V, VII). It is only necessary 
to recall the main points. The upper and lower surfaces of the leaf are 
provided with a layer of cells usually devoid of chlorophyll. The mesophyll 
of the leaf consists usually of a layer of palisade cells beneath the epider- 
mis, and the remainder consists of loose parenchyma with large intercel- 
lular spaces. Through the mesophyll course the "veins," or fibro-vas- 
cular strands, consisting of the xylem and phloem portions and serving 
as conduits for water, salts, and foodstuffs. In the epidermis are the 
stomata, each one protected by the two guard cells. The guard cells as 
well as the mesophyll contain chlorophyll. The stomata and the com- 
municating intercellular spaces furnish the avenues for the ingress and 
egress of gases, and for the escape of water vapor. 

761. Protection of leaves. — There are many modifications of the general 
plan of structure in different leaves, many of them being adaptations for 
the protection of the leaf under adverse or trying conditions. Many 
leaves are also capable of assuming certain positions which afford them 
protection. The discussion of this subject may be presented under two 
general heads: Protective modifications ; protective positions. 



39 2 RELATION TO ENVIRONMENT. 

II. Protective Modification of Leaves. 

762. General directions in which these modifications have 
taken place. — The usual type of foliage leaf selected is that of 
deciduous trees or shrubs or of our common herbs. Such a 
leaf is usually greatly expanded and thin in order to present as 
great a surface as possible in comparison with its mass, since 
the kind of work which the leaf has to do can be more effectu- 
ally carried on when it possesses this form. This form of leaf 
is best adapted for work in regions where there is a medium 
amount of moisture such as exists in the temperate zones. But 
since there are very great variations in the climatic and soil 
conditions of these regions, and even greater changes in desert 
and arctic regions, the type of leaf described is unsuited for 
all. Its own life would be endangered, and it would also en- 
danger the life of the plant. Modifications have therefore taken 
place to meet these conditions, or at least those plants whose 
leaves have become modified in those directions which are 
suited to the surrounding conditions have been able to persist. 
Excessive cold or heat, drought, winds, intense light, rain, etc., 
are some of the conditions which endanger leaves. The pro- 
tective modifications of leaves may be grouped under four gen- 
eral heads: (i) Structural adaptations; (2) Protective cover- 
ing; (3) Reduction of surface; (4) Elimination of the leaf through 
the complete assumption of the leaf function by the stem. 

763. (1) Structural adaptations. — The general structure of 
the leaf presents certain features which are protective. The pali- 
sade layer of cells found usually beneath the upper epidermis 
forms a compact layer of long cells which not only acts as a 
light screen cutting off a certain amount of the light, since too 
intense light would be harmful ; it also aids in lessening the loss 
of water from the upper surface, where radiation is greater. 
The stomata are usually on the under side of aerial leaves, and 
the mechanism which closes them when the leaf is losing too 
much water is protective. As a protection against intense light 
the number of palisade layers is sometimes increased or the 



FOLIAGE LEAVES. 



393 




cells of this layer are narrow and long. This is often beauti- 
fully shown when comparing 

leaves of the same plant grown 

in strong light with those grown 

in the shade. The compass 

plant (Lactuca scariola) affords 

an interesting example. The 

leaves grown in the light are 

usually vertical, so that the light 

reaches both sides. Such leaves 

often have all of the mesophyll 

organized into palisade cells (fig. 

435), while leaves grown in the 

deep shade may have no palisade 

cells. 

764. (2) Protective covering. 
— Epidermis and cuticle. — The 
walls of the epidermal cells are 
much thickened in some plants. 
Sometimes this thickening occurs 
in the outer wall, or both walls 
may be thickened. Variation in 
this respect as well as the extent 
of the thickening occur in dif- 
ferent plants and are often corre- 
lated with the extremes of conditions which they serve to meet. 
The cuticle, a waxy exudation from the thick wall of the epider- 
mis of many leaves, also serves as a protection against too great 
loss of water, or against the leaf becoming saturated with water 
during rains. The cabbage, carnation, etc., have a well-developed 
cuticle. The effect of the cuticle in shedding water can be nicely 
shown by spraying water on a cabbage leaf or by immersing it in 
water. Sunken stomata also retard the loss of water vapor. 

Covers of hair or scales. — In many leaves certain of the cells 
of the epidermis grow out into the form of hairs or scales of 
various forms, and they serve a variety of purposes. When 




Fig. 435- 
Structure of leaf of Lactuca scariola. 
Upper one grown in sunlight, palisade 
cells on both sides. Lower one grown 
in shade, no palisade tissue. 



394 RELATION TO ENVIRONMENT. 

the hairs form a felt-like covering as in the common mullein 
some antennarias, etc., they lessen the loss of water vapor be- 
cause the air-currents close to the surface of the leaf are retarded. 
Spines (see the thistles, etc.) also afford a protection against 
certain animals. 

765. (3) Reduction of surface. — Reduction of leaf surface is 
brought about in a variety of ways. There are two general 
modes: (1st) Reduction of surface along with reduction of 
mass; (2d) Reduction of surface inversely as the mass. Ex- 
amples of the first mode are seen in the dissected leaves of many 
aquatic plants. In this finely dissected condition the mass of 
of the leaf substance is much reduced as well as the leaf surface, 
but the leaf is less liable to be injured by movement of the water. 
In addition it has already been pointed out that lobed and 
divided aerial leaves are much less liable to injury from violent 
movements of the air, than if a leaf with the same general out- 
line were entire. The needle leaves of the conifers are also 
examples, and they show as well structural provisions for pro- 
tection in the thick, hard cell-walls of the epidermis. To off- 
set the reduced surface there are numerous crowded leaves. 
Reduction of surface inversely as the mass, i.e., the mass of 
the leaf may not be reduced at all, or it may be more or less 
increased. In other words, there is less leaf surface in pro- 
portion to the mass of leaf substance. It is probable in many 
cases, example: the crowded, overlapping small scale leaves of 
the juniper, arbor vitae, cypress, cassiope, pyxidanthera, etc., that 
there has been a reduction in the size of the leaf, and at the 
same time an increase in thickness. This with the crowding 
together of the leaves and their thick cell-walls greatly lessens 
the radiation of moisture and heat, thus protecting the leaves 
both in dry and cold weather. The succulents, like " live-for- 
ever," have a small amount of surface in proportion to the mass 
of the leaf. In the yucca, though the leaves are often large, 
they are very thick and expose a comparatively small amount 
of surface to the dry air and intense sunlight of the desert regions. 
The epidermal covering is also hard and thick. In addition. 



FOLIAGE LEAVES. 



395 



such leaves, as well as those of many succulents, are so thick 
they provide water storage sufficient for the plants, which radi- 
ate so slowly from their surface. 

766. (4) Elimination of the leaf. — Perhaps the most striking 
illustration of the reduction of leaf surface is in those cases where 




Fig. 436. 
A "Phylloclade," leaves absent, stems broadened to function as leaves, on the 
edges numerous flowers are borne. 

the leaf is either completely eliminated as in certain euphorbias, 
or in certain of the cacti where the leaves are thought to be re- 
duced to spines. Whether the cactus spine belongs to the leaf 
series or not, the leaf as an organ for assimilation and trans- 
piration has been completely eliminated and the same is true 
in the phylloclades. The leaf function has been assumed by 
the stem. The stem in this case contains all the chlorophyll; 
is bulky, and provides water storage. 

III. Protective Positions. 

767. In many cases the leaves are arranged either in relation 
to the stem, or to each other, or to the ground, in such a way 
as to give protection from too great radiation of heat or moisture. 
In the examples already cited the imbricated leaves of cassiope, 



39^ DELATION TO ENVIRONMENT 

pyxidanthera, juniper, etc., come also under this head. In the 
junipers the leaves spread out in the summer, while in the winter 
they are closely overlapped. An interesting example of protective 
position is to be seen in the case of the leaves of the white pine. 
During quite cold winter weather the needles are appressed to 
the stem, and sometimes the trees present a striking appear- 
ance in contrast with the spreading position of the needles in 
summer. On windy days in winter, the needles turn with the 
wind and become rigid in that position so that they remain 
in a horizontal position for some time, often until the wind 
dies down, or until milder weather. The following day, should 
there be a cold strong wind from the opposite direction, the 
needles again assume a leeward direction. In quiet weather 
appressed to the stem and in the form of a brush there is less 
radiation of heat than if they diverged. In strong winds by 
turning in the leeward direction the wind is not driven between 
the needle bases and scales. Some plants, especially many 
of those in arctic and alpine regions, have very short stems and 
the leaves are developed near the ground, or the rock. Lying 
close on the ground they do not feel the full force of the drying 
winds, there is less radiation from them, and the radiation of 
heat from the ground protects them. Many plants exhibit 
movement in response to certain stimuli which place them in 
a position for protection. Some of these examples have been 
discussed under the head of irritability (see Chapter XIII). The 
night position of leaves and cotyledons presented by many 
plants, but especially by many of the Leguminosae, is brought 
about by the removal of the light stimulus at evening. In many 
leaves, when the light influence is removed, the influence of 
growth turns the leaves downward, or the cotyledons of some 
plants upward. In this vertical position of the leaf-blade there 
is less radiation of heat during the cool night. The most strik- 
ing cases of protection movements are seen in the sensitive 
plant. As we have seen, the leaves of mimosa close in a verti- 
cal position at midday if the light and heat are too strong. Ex- 
cessive transpiration is thus prevented. At night the vertical 






FOLIAGE LEAVES. 



397 



position prevents excessive radiation of heat. The vertical or 
profile position of the leaves of the compass plant already re- 
ferred to not only lessens transpiration, but the intense heat and 
light of the midday sun is avoided. This profile position is 
characteristic of certain plants in the dry regions of Australia, 
and the topmost leaves of tropical forests. 

IV. Relation of Leaves to Light. 

768. It is very obvious from our study of the function of the 

foliage leaf that its most important relation to environment is 

that which brings it in touch with light and air. It is necessary 

that light penetrate the leaf tissue that the gases of the air and 




Fig. 437 
Mosaic form by trailing shoots of Panicum variegatum, "ribbon grass." 

plant may readily diffuse and that water vapor may pass out 
of the leaf. The thin expanded leaf-blade is the most economi- 
cal and efficient organ for leaf work. We have seen that leaves 
respond to light stimulus in such a way as to bring their upper 
sides usually to face the source of light, at right angles to it or 
nearly so (heliotropism, see Chapter XIII). How fully this is 
brought about depends on the kind of plant, as well as on other 
elements of the environment, for as we have seen in our study of 
leaf protection there is danger to some plants in any region, 



39^ RELATION TO ENVIRONMENT. 

and to other plants in certain regions that the intense light 
and heat may harm the protoplast, or the chlorophyll, or both. 

The statement that leaves usually face the light at right angles 
is to be taken as a generalized one. The source of the strongest 
illumination varies on different days and again at different times 
of the day. On cloudy days the zenith is the source of strongest 
illumination. The horizontal position of a leaf, where there are 
no intercepting lateral or superior objects would receive its 
strongest light rays perpendicular to its surface. The fact is, 
however, that leaves on the same stem, because of taller or 
shorter adjacent stems, are so situated that the rays of greatest 
illuminating power are directed at some angle between the 
zenith and horizon. Many leaves, then, which may have their 
upper sides facing the general source of strongest illumination, 
no not necessarily face the sun, and they are thus protected 
from possible injury from intense light and heat because the 
direct rays of sunlight are for the most part oblique. This 
does not apply, of course, to those leaves which " follow the 
sun" during the day. Their specific constitution is such that 
intense illumination is beneficial. 

The leaf is adjusted as well as may be in different species of 
varying constitution, and under different conditions, to a certain 
balance in its relation to the factors concerned. The problem 
then is to interpret from this point of view the positions and 
grouping of leaves. Because of the specific constitution of dif- 
ferent plants, and because of a great variety of conditions in the 
environment, we see that it is a more or less complex question. 

769. Day and night positions contrasted. — In many plants 
the day and night positions of the leaves are different. At 
night the leaves assume a position more or less vertical, known 
as the profile position. This is generally regarded as a pro- 
tective position, since during the cool of the night the radiation 
of heat is less than if the leaf were in a vertical position. In 
many of these plants, however, the leaves in assuming the night 
position become closely appressed which would also lessen the 
radiation. This peculiarity of leaves is largely possessed by 



FOLIA G£ LEAVES, 



399 



the members of the family Leguminoseae (clovers, peas, beans, 
etc.), and by the sensitive plants.* But it is also shared by 
some other plants as well (oxalis, for example). The leaves 
of these plants are usually provided with a mechanism which 
enables them to execute these movements with ease. There is 
a cushion {pulvinus) of tissue at the base of the petiole, and in 
the case of compound leaves, at the base of the pinnae and pin- 
nules which undergoes changes in turgor in its cells. The col- 
lapsing of the cells by loss of water into the intercellular spaces 
causes the leaf to droop. When the cells regain their turgor 
by the absorption of the water from the intercellular spaces the. 
leaf is raised to the horizontal, or day position. The light stirris 
ulus induces turgor of the pulvinus, the disappearance of the stim- 




Fig. 438. 
Sunflower with young head turned toward morning sun. 

ulus is accompanied by a loss of turgor. It is a remarkable 
fact that in some sensitive plants, intense light stimuli are alarm 
signals which result in the same movement as if the light stim- 

* The most remarkable case is that of the "telegraph" plant (Des- 
modium gyrans). Aside from the day and night positions which the 
leaves assume, there is a pair of small lateral leaflets to each leaf which con- 
stantly execute a jerky motion, and swing around in a circle like the second 
hand of a watch. 



4oo 



RELATION TO ENVIRONMENT. 



ulus were entirely removed. As we know also contact or pres- 
sure stimulus, or jarring produces the same result in "sensitive" 
plants like mimosa, some species of rubus, etc. In many plants 
there is no well-developed pulvinus, and yet the leaves show 
similar movements in assuming the day and night positions. 
Examples are seen in the sunflower, and in the cotyledons of 
many plants. A little observation will enable any one interested 
to discover some of these plants.* In these cases the night 
position is due to epinastic growth, and while this influence is 
not removed during the day the light stimulus overcomes it 
and the leaf is raised to the day position. 

770. Leaves which rotate with the sun. — During the growth 
period the leaves of the sunflower as well as the growing end 







Fig. 439- 
Same sunflower plant photographed just at sundown. 



of the stem respond readily to the direct sunlight. The re- 
sponse is so complete that during sunny days the leaves toward 
the growing end of the stem are drawn close together in the 
form of a rosette and the entire rosette as well as the end of the 



* Seedlings are usually very sensitive to light and are good objects to 
study. 



FOLIAGE LEAVES. 



401 



stem are turned so that they face the sun directly. In the morn- 
ing under the stimulus of the rising sun the rosette is formed 
and faces the east. All through the day, if the sun continues to 
shine, the leaves follow it, and at sundown the rosette faces 
squarely the western horizon. For a week or more the young 
sunflower head will also face the sun directly and follow it all 
day as surely as the rosette of leaves. At length, a little while 
before the flowers in the head blossom, the head ceases to turn, 




Fig. 440. 
Same plant a little older when the head does not turn, but the stem and leaves do. 

but the rosette of leaves and the stem also, to some extent, con- 
tinue to turn with the sun. When the leaves become mature 
they also cease to turn. This is well shown in all three photo- 
graphs (figs. 438-439). The lower leaves on the stem being 
older have assumed the fixed horizontal position usually char- 
acteristic of the plant with cylindrical habit. 

It is not true, as is commonly supposed, that the fully opened 
sunflower head turns with the sun. But I have observed young 
heads four or five inches in diameter rotate with the sun all day. 
This is because the growing end of the stem as well as the young 
head responds to the light stimulus. So there is some truth as 
well as a great deal of fiction in the popular belief that the sun- 



4&2 RELATION TO ENVIRONMENT. 

flower head follows the sun. The young head will follow the 
sun all day even if all the leaves are cut off, and the growing 
stem will also if all the leaves as well as the flower head are cut 
away. Young seedlings will also turn even if the cotyledons and 
plumule are cut off. 

This phenomenon of the rotation of leaves with the sun is 
much more general than one would infer, as may be seen from 
a little careful observation of rapidly growing plants on bright 
sunny days. In Alabama I have observed beautiful rosettes of 
Cassia marilandica rotate with the sun all day. The peculiarity 
is very striking in the cotton plant, especially when the rows 
extend north and south. In the forenoon or afternoon it is 
most striking as the entire row shows the leaves tilted up facing 
the sun. There are many of our weeds and common flowers 
of field and garden which show this rotation of the leaves. Some 
of these form rotating rosettes; while in others the leaves rotate 
independently as in the sweet clover. 

771. Fixed position of old leaves. — In many of the cases cited 
in the preceding paragraph, the rotation of the leaf only occurs 
on sunny days. During cloudy days the leaves of the sunflower, 
for example, are in a nearly horizontal position, or the lower 
ones may be somewhat oblique, since the stronger illumination on 
such a plant would be the oblique rays rather than the zenith 
rays. As the leaves reach maturity also the epinasitic growth is 
equalized by hyponastic growth so that the growth movements 
bring the leaf to stand in a nearly horizontal position, or that 
position in which it receives the best illumination. In age, then, 
many leaves have a fixed position and this corresponds with the 
position assumed on cloudy days. 

772. Position on horizontal stems. — On horizontal stems the 
leaves have a horizontal position, and if such a stem is stood in 
an erect position the appearance is very odd. If the leaf arises 
directly from the horizontal stem, its petiole will be twisted part 
way around in order to bring the face of the leaf uppermost. 
It is interesting to observe the different relation of stem, petiole 
and blade and the amount of twisting as the horizontal stem or 



FOLIAGE LEA FES. 4^3 

vine trails over irregularities in the surface, or climbs over and 
through other vegetation. 

773. Position of leaflets on divided leaves. — An interesting 
comparison can be made with entire, lobed, divided and dis- 
sected leaves. The entire leaf usually lies in one plane, since 
usually the problem of adjustment is the same for the entire 
surface. So the lobes of a leaf usually lie all in the same plane 
as they would if the leaf were entire. We find the same is true 
usually of the compound leaf. It forms an incomplete mosaic. 
Some of the pieces having been removed allow much of the light 
to pass through to leaves beneath. Leaves, especially those of 
some size rarely lie in a flat plane. Some are more or less de- 
pressed. Some curve downward. Compound leaves often 
curve more or less and the leaflets often droop more or less in a 
graceful fashion. It is interesting, however, that these far-sepa- 
rated leaflets all He in the same general plane. This is because 
the area of the leaf, if not too large, makes the problem of posi- 
tion with reference to light much the same as if the leaf were 
entire. The leaflets or divisions, though separated, are laminate, 
and they can work more efficiently facing the light. But suppose 
we extend our observation to the finely dissected capillary leaves 
of some of the parsley family (Umbelliferae), or to the upper 
leaves of the fennel-leaved thoroughwort (Eupatorium fceni- 
culaceum) among the aerial plants, and to Myriophyllum among 
the aquatic plants. The divisions are threadlike or cylindrical. 
One side of the leaflet is just as efficient when presented to the 
light as another. As a result the leaflets are not arranged in 
the same plane, but stand out in many directions. 

Occasionally one finds a divided or compound leaf in such a 
position that one portion, because of being shaded above, receives 
the stronger fight stimulus from the side, while the other portion 
is lighted from above. If this relation continues throughout 
the growth-period of the leaf the leaflets of one portion may lie 
in a different plane from those of the other portion. In such 
cases, some of the leaflets are permanently twisted to bring them 
into their proper light relation. 



404 RELATION TO ENVIRONMENT. 

V. Leaf Patterns. 

MOSAICS, OR CLOSE PATTERNS. 

774. Where the leaves of a plant, or a portion of a plant, are 
approximate and arranged in the form of a pattern, the leaves 
fitting together to form a more or less even and continuous sur- 
face, such patterns are sometimes termed " mosaics," since the 
relation of leaves to one another is roughly like the relation of 
the pieces of a mosaic. A good illustration of a mosaic is pre- 
sented by a greenhouse plant Fittonia (fig. 441). The stems 




Fig. 441. 
Fittonia showing leaves arranged to form compact mosaic. The netted vena- 
tion of the leaf is very distinctly shown in this plant. (Photo by the Author.) 

are prostrate and the erect branches quite short, but it may 
have quite a wide system by the spreading of the runners; the 
branches of such a length that the leaves borne near the tips all 
fit together forming a broad surface of leaves so closely fitted 
together often that the' stems cannot be seen. The advantage 
of a mosaic over a separate disposition of leaves at somewhat 
different levels is that the leaves do not shade one another. Were 
all the light rays coming down at right angles to the leaves, there 
would not be any shading of the lower ones, but the oblique 
rays of light would be cut off from many of the leaves. In the 
case of a mosaic all the rays of light play upon all the leaves. 
Some of the mosaics which can be observed are as follows: 



FOLIAGE LEAVES. 



405 




775. Rosette pattern. — The rosette pattern is presented by 
many plants with "radial" leaves, or leaves which arise in a 
cluster near the surface 

of the ground, and are 
thus more or less crowded 
in their arrangement on 
the stem. The pretty 
gloxinia often presents 
fine examples of a loose 
rosette. In the rosette 
pattern the petioles of 
the lower leaves are 
longer than the upper 
ones, and the blade is 
thus carried out beyond 
the inner 'eaves. The 
leaves being so crowded 
in their attachment to 
the stem He very nearly 
in the same plane. 

776. Vines and climbers. — Some of the most extensive mosaic 
patterns are shown in creeping and climbing vines. A very 
common example is that of the ivies trained on the walls of build- 
ings, covering in some instances many square yards of surface. 
Where the vines trail over the ground or clamber over other 
vegetation, it is interesting to observe the various patterns, and 
the distortion of petioles brought about by turning of the leaves. 
Of examples found in greenhouses, the Pellonia is excellent, and 
the trailing ribbon-grass often forms loose mosaics. 

777. Branch patterns. — These patterns are very common. 
They are often formed in the woods on the ends of branches by 
the leaves adjusting themselves so as to largely avoid shading 
each other. Figure 443 illustrates one of them from a maple 
branch. It is interesting to note the way in which the leaves 
fit themselves in the pattern, how in some the petioles have 
elongated, while others have remained short. Of course, it 



Fig. 442. 
Rosette pattern of leaves. 



406 



RELATION TO ENVIRONMENT. 




Fig. 443- 
Spray of leaves of striped maple, showing different lengths of leafstalks. 




Fig. 444. 
Cedar of Lebanon, strong light only from one side of tree (Syria). 



FOLIAGE LEAVES. 



407 



should be understood that the pattern is made during the growth 
of the leaves. 

778. The tree pattern. — Mosaics are often formed by the 
exterior foliage on a tree, though they are rarely so regular as 
some of those mentioned above. Still it is common to see in some 
trees with drooping limbs like the elm, beautiful and large mo- 
saics. The weeping elm sometimes forms a very close and 
quite even pattern over the entire outer surface. In most trees 
the leaf arrangement is not such as to form large patterns, but 
is more or less open. While the conifers do not form mosaics 
there are many interesting examples of grouping of foliage on 
branch systems into broadly expanded areas, as seen in the 
branches of white pine trees, especially in the edge of a wood, 
or as seen in the arbor vitae. 

OTHER PATTERNS. 

779. Imbricate pattern of short stems. — This pattern is quite 
common, and differs from the rosette in that the leaves are dis- 
tributed further apart on 

the stem so that the cen- 
tral ones are consider- 
ably higher up than in 
the mosaic. The lower 
petioles are longer, as in 
the rosette, so that the 
outer lower leaves ex- 
tend further out. Some 
begonias show fine im- 
bricate patterns. 

780. Spiral patterns. 
— They are very common 
on stems of the cylindrical 
type, which are unbranched, or but little branched. The sun- 
flower, mullein, chrysanthemum, as it is grown in greenhouses, the 
Easter lily, etc., are examples. The spiral arrangement of the 
leaves provides that each successive leaf on the stem, as one ascends 
the stem, is a little to one side so that it does not cast shade on the 







1 




0^^mNn 





Fig. 445- 
Imbricate pattern of leaves; Begonia. 



408 



RELATION TO ENVIRONMENT. 



leaf just below. In some stems, according to the leaf arrange- 
ment (or phyllotaxy), one would pass several times around in 
ascending the stem before a leaf would be found directly above 
another, which would be such a distance below that it would not 
be shaded to an appreciable extent. Interesting observations 
can be made on different plants to work out the relation of dis- 
tance of leaves on the stem to length of the upper and lower 



- ^ 
















* v '\>^ '■•'•' ■,"!. ^'.*:V . -".' ."^ 




S\ . *'* 




.. 




> £2feg|s§i 




H 


yjfm-.y * 


. •' 







Fig. 446. 
Palm showing radiate arrangement of leaves and the petiole of the leaf func- 
tions as stem in lifting leaf to the light. 

leaves; the number of vertical rows on the stem compared to 
the width of the leaves; and the relation of these facts to the 
problem of light supply. Related to the spiral pattern is that of 
erect stems with opposite leaves. Here each pair is set at right 
angles to the direction of the pair above or below. 

781. Radiate pattern. — This pattern is present in many grasses 
and related plants with narrow leaves and short stems. The 
leaves are often very crowded at the base, but by radiating in 
all directions from the horizontal to the vertical, abundant ex- 



nrmTTi 



FOLIAGE LEAVES. 



409 



posure to light is gained with little shading. The dragon tree 
screw-pine, and plants grown in greenhouses also illustrate this 




Fig. 447. 
Screw pine (Pandanus) showing prop roots and radiate pattern of leaves. 

type. It is also shown in cycads, palms, and many ferns, although 
these have divided leaves. 

782. Compass plants. — These plants with vertical leaf arrange- 
ment, and exposure of both surfaces to the lateral rays of light 
have been mentioned in other sections (Lactuca scariola). 

783. Open patterns. — Open patterns are presented by divided 
or "branched" leaves. Where the leaves are very finely dis- 
sected, they may be clustered in great profusion and yet admit 
sufficient light for some depth below. Where the leaflets are 
broader, the leaves are likely to be fewer in number and so 
arranged as to admit light to a great depth so that successive 
leaves below on the same or adjacent stems may not be too much 
shaded. On such plants, often the leaves lying next the ground 
are entire or less divided. 



CHAPTER XLI. 

THE ROOT 

I. Function of Roots. 

784. The most obvious function of the roots of ordinary plants 
are two: ist, To furnish anchorage and partial support, and 
2d, absorption of liquid nutriment from the soil. The environ- 
mental relation of such roots, then, in broad terms, is with the 
soil. It is very clear that in some plants the root serves both 
functions, while in other plants the root may fulfil only one of 
these requirements. 

The problems which the plant has to solve in working out 
these relations are: 

(i) Permeation of the soil or substratum. 

(2) Grappling the substratum. 

(3) A congenial moisture or water relation. 

(4) Distribution of roots for the purpose of reaching food- 
laden soil. 

(5) Exposure of surface for absorption. 

(6) The renewal of the delicate structures for absorption. 

(7) Aid in preparation of food from raw material. 

(8) The maintenance of the required balance between the 
environment as a whole and the increasing or changing require- 
ments of the plant. 

785. (1) Permeation of the soil or substratum. — The funda- 
mental divergence of character in the environmental relations of 
root and stem are manifest as soon as they emerge from the 
germinating seed. Under the influence of the same stimulus 
(gravity) the root shows its geotropic character by growing down- 

410 



ROOTS. 4 11 

ward, while the geotropic character of the stem is shown in its 
upward growth. 

The medium which the root has to penetrate offers consider- 
able resistance, and the form of the root as well as its manner of 
growth is adapted to overcome this difficulty. The slender, 
conical, penetrating root-tip wedges its way between the minute 
particles of soil or into the minute crevices of the rock, while 
the nutation of the root enables it to search for the points of least 
resistance. The root-tips having penetrated the soil, the older 
portions of the root continue this wedge action by growth in 
diameter, though, of course, elongation of the old parts of the 
root does not take place. It is the widening growth of the taper- 
ing root that produces the wedge-like action. The crevices of 
the rock are sometimes broadened, but the resistance here is so 
great, the root is often greatly flattened out. 

786. (2) Grappling the substratum. — The mere penetration 
of a single root into the soil gives it some hold on the soil and it 
offers some resistance to a "pull" since it has wedged its way in 
and the contact of soil particles offers resistance. The root-hairs 
formed on the first entering root growing laterally in great num- 
bers and applying themselves very closely to the soil particles, 
increase greatly the hold of the plant on the soil, as one can 
readily see by pulling up a young seedling. Lateral roots are 
soon formed, and as these continue to extend and ramify in all 
directions, the hold is increased until in the case of some of the 
larger plants the resistance their hold would offer would equal 
many tons. Even in some of the smaller shrubs and herbs the 
resistance is considerable, as one can easily test by pulling with 
the hand. To obtain some idea of the amount of resistance the 
roots of these smaller plants offer, they can be tested by pulling 
with the ordinary spring scales. 

787. (3) A congenial moisture, or water relation. — In gen- 
eral, the roots seek those portions of the soil provided with a modi- 
cum of moisture. Usually a suitable moisture condition is present 
in those portions of the soil containing the plant food. But if por- 
tions of the soil are too dry and very nearby other portions con- 



412 RELATION TO ENVIRONMENT. 

taining moisture, the roots grow mainly into the moist substratum 
{hydrotropism). If the soil is too wet, the roots grow away from 
it to soil with less water, or in pom^ cases will grow to and upon 
the surface of the soil. 

The roots need aeration, and where the supply of water is too 
great, the air is shut out, and we know that corn, wheat, and 
many other plants become "sickly" in low and undrained soil 
in wet seasons. This can only be said in the case of our ordinary 
dry land plants, i.e., those that occupy an intermediate position 
between water-loving plants and dry-conditioned plants. This 
phase of the subject must be reserved for special treatment. 
(See Chapter XLVI.) 

788. (4) Distribution of roots for the purpose of reaching 
food-laden soil. — This is one of the essential relations of the root 
in the case of the land plant, and probably accounts for the very 
extensive ramification of the roots. To some extent it also 
explains the different root systems in some plants. The pines, 
spruces, etc., usually grow in regions where the soil is very shal- 
low. The root system does not extend deeply into the soil. It 
spreads laterally and extends widely through the shallow surface 
soil and presents a very different aspect from the stem system in 
the air. The root-system of the broad-leaved trees usually extends 
more deeply into the soil, while of course, extending laterally 
to great distances. The hickory, walnut, etc., especially have 
strong tap roots which extend deeply into the soil, and the root 
system of such a tree is more comparable in aspect, if it were 
entirely uncovered, to the stem system in the air. The tap-root 
is more pronounced in some trees than in others. It may be that 
in the hickory and walnut the deep tap-root is important in 
supplying the tree with water in dry seasons, especially when 
growing on dry, gravelly soil which does not retain moisture on 
the surface nor hold it within two or three feet of the surface. 
Experiment has demonstrated, by pot culture of plants, that 
where soil rich in plant food lies adjacent to poor soil, no matter 
in what part of the pot the rich soil is, the greatest growth and 
branching of roots is in the rich soil, 



ROOTS. 413 

789. (5) Exposure of root surface for absorption. — The prin- 
cipal part of root absorption takes place in the young root and 
the root hairs growing near the root- tip. The root-tips and 
root-hairs in their relation to the root systems on which they are 
borne are not to be compared morphologically with the leaves 
and stem system. But the root-tips and hairs are absorbing 
organs of the roots while the main root system supports them, 
brings them into relation with the soil and moisture, and con- 
ducts food and other substances to and from them. One of the 
important relations of the leaf is that of light, and since the source 
of light is restricted, i.e., it is not equally strong from all sides, 
an expanded and thin leaf-blade is more effective than an equal 
expenditure of plant material in the form of thread-like out- 
growths. It is different, however, with the plant food dissolved 
in the soil water. It is equally accessible on all sides. A greater 
surface for absorption is exposed with the same expenditure of 
material by multiplication of the organs and a reduction in their 
size. Numerous delicate root-hairs present a greater absorbing 
surface than if the same amount of material were massed into 
leaflike expansions. There is another important advantage 
also. Its slender roots and thread-like root-hairs allow greater 
freedom of circulation of water, food solutions, and air than if 
the absorbing organs of the roots were broadly expanded. 

790. (6) The renewal of the delicate structures for absorp- 
tion. — The delicate root-hairs are easily injured. The thin 
cell-walls through which food solutions flow become more or less 
choked by the gradual deposit of substances in solution in the 
water, and continued growth of the root in diameter forms a 
firmer epidermis and cortex through which the solutions taken 
up by the root-hairs would pass with difficulty. For this reason 
new root-hairs are constantly being formed on the growing root- 
tip throughout the growing season, and in the case of perennial 
plants, through each season of their growth. 

791. (7) Aid in preparation of food from raw materials. — For 
most plants the food obtained from the soil is already in solution in 
the soil water. But there are certain substances (examples, some 



41 4 RELATION TO ENVIRONMENT. 

of the chemical compounds of potash, phosphoric acid, etc.) which 
are insoluble in water. Certain acids excreted by the roots aid 
in making these substances soluble (see Chapter III). In a num- 
ber of plants the roots have become associated with fungus or 
bacterial organisms which assist in the manufacture of nitro- 
genous food substances, or even in the absorption of ordinary- 
food solution from the soil, or in making use of the decaying 
humus of the forest (see Chapter IX). 

792. (8) The maintenance of the required balance between 
the environment and the increasing or changing requirements 
of the plant. — In this matter the entire plant participates. Men- 
tion is made here only of the general relation which the root 
sustains to its own environment and the increased burden placed 
upon it by the shoot. The increase in the root system keeps 
pace with the increasing size of the stem system. The roots 
become stronger, their ramifications wider, and the number of 
absorbing rootlets more numerous. The observation is some- 
times offered that the correlation between the root system of a 
plant, and the form of the stem system and position of the leaves, 
is of such a nature that plants with a tap-root system have their 
leaves so arranged as to shed the water to the center of the sys- 
tem, while plants with a fibrous root system have their leaves so 
arranged as to shed the water outward. In support of this 
attention is called to the radiate type of the leaf system of the 
dandelion, beet, etc. In the second place the imbricate type as 
manifested in broad-leaved trees, and in the overlapping branch 
systems of many pines, etc. One should note, however, that in 
the former class the leaves are often arranged to shed as much 
water outward as inward. As to the latter class, there is need 
of experiment to determine whether these empirical observations 
are correct, for the following reasons: ist, Root and leaf distri- 
bution are governed by other and more important laws, the root 
being influenced by the location of food in the soil which usually 
forms a very thin stratum while the shoot and leaf is mainly in- 
fluenced by light, and root distribution is much wider in a lateral 
direction than that of the branches. 2d, In light rains the leaf 



ROOTS. 4 J 5 

surface holds back practically all the rain which is then evap- 
orated into the air and lost to the root systems. 3d, In heavy 
and long-continued rains the water breaks through the leaf 
system to such an extent that roots under the tree would be as 
well supplied as those outside, and the ground outside being 
saturated anyway, the roots do not need the small additional 
water which may have been shed outward. 4th, It is the habit 
of plants where left undisturbed (except in rare cases), to grow 
in more or less dense formations or societies. Here there is no 
opportunity for any appreciable centrifugal distribution of rain- 
fall and yet the root distribution is practically the same, except 
that the root systems of adjacent plants are interlaced. 

II. Kinds of Roots. 

793. The root system. — From the foregoing, it will be under- 
stood that the roots of a plant taken together form the root sys- 
tem of that plant. In soil roots in general we usually recognize 
two kinds of root systems. 

794. The fibrous-root system. — Roots which are composed of 
numerous slender branching roots resembling "fibers," are 
termed fibrous, or the plant is said to have a fibrous-root system. 
The bean, corn, most grasses, and many other plants have fibrous- 
root systems. 

795. The tap-root system. — Plants with a recognizable cen- 
tral shaft-like root, more or less thickened and considerably 
stouter than the lateral roots, are said to have tap roots, or they 
have a tap-root system. The dandelion, beet, carrot (see crown 
tuber) are examples. The hickory, walnut, and some other 
trees have very prominent tap-roots when young. The tap-root 
is maintained in old age, but the lateral roots often become 
finally as large as the tap-root. Besides tap-roots and fibrous- 
roots, which include the larger number, several other kinds of 
roots are to be enumerated. 

796. Aerial roots. — Aerial roots are most abundantly devel- 
oped in certain tropical plants, especially in the orchids and 
aroids. Many examples of these plants are grown in conserva- 



416 



RELATION TO ENVIRONMENT. 



tories. The amount of moisture is. so great in these tropical 
regions that the roots are abundantly supplied without the soil 
relation. Certain of the roots hang free in the air and are pro- 
vided with a special sheath of spongy tissue called the velamen, 
through which moisture is absorbed from the air. Other roots 
attach themselves to the trunk or branches of the tree on which 
the orchid is growing, and furnish the support to the epiphyte, 
as such plants are often called. Among the tangle of these 
clinging roots falling leaves are caught. Here they decay and 
nourishing roots grow from the clinging roots into this mass of 
decaying leaves and supply some of the plant food. Aerial 
roots sometimes possess chlorophyll. 

There are a number of plants, however, in temperate regions 
which have aerial roots. These are chiefly used to give the stem 
support as it climbs on trees or on walls. They are sometimes 
called clinging roots. A common example is the climbing poison 
ivy (Rhus radicans), the trumpet creeper, etc. Such aerial roots 
are called adventitious roots. 

797. Bracing roots, or prop roots. — These are developed in a 
great variety of plants and serve to brace or prop the plant where 

the fibrous-root system is in- 
sufficient to support the heavy 
shoot system, or the shoot sys- 
tem branches so widely props 
are needed to hold up the 
branches. In the common In- 
dian corn several whorls of 
bracing roots arise from the 
nodes near the ground and ex- 
tend outward and downward to 
the ground, though the upper 
whorls do not always succeed in 
reaching the ground. The 
screw-pine so common in 
greenhouses affords an excellent example of prop roots. The 
roots are quite large, and long before the root reaches the soil the 




Fig. 448. 
Bracing roots of Indian corn. 



ROOTS. 



417 



large root-cap is evident. The banyan tree of India is a classic 
example of prop roots for supporting the wide-reaching branches. 
The mangrove in our own subtropical forests of Florida is a 
nearer example. 

798. Buttresses are formed at the junction of the root and 
trunk, and therefore are part root and part stem. Splendid 




Fig. 449- 
Buttresses of silk-cotton tree, Nassau. 

examples of buttresses are formed on the silk-cotton tree. They 
are sometimes formed on the elm and other trees in low swampy 
ground. 

799. Fleshy roots, or root tubers. — These are enlargements of 
the root in the form of tubers, as in the sweet potato, the dahlia, 
etc. They are storage reservoirs for food. Portions of the roots 
become thick and fleshy and contain large quantities of sugar, 
as in the sweet potato, or of inidin (a carbohydrate) in the root- 
tubers of the dahlia and other composites. 

800. Water roots and roots of water plants. — These are roots 
which are developed in the water, or in the soil. Water-roots 
are sometimes formed on land plants where the root comes in 



41 8 RELATION TO ENVIRONMENT. 

contact with a body of water, or a stream. Water-roots usually 
possess no root-hairs, or but a few, as can be seen by comparing 
water-roots with soil-roots, or by comparing roots of plants 
grown in water cultures. The greater body of water in contact 
with the root and the more delicate epidermis of the root render 
less necessary the root-hairs. The duck-meats (Lemna) are 
good examples of plants having only water-roots. Other aquatic 
plants like the potamogetons, etc., have true roots which grow 
into the soil and serve to anchor the plant, but they are not devel- 
oped as special organs of absorption, since the stem and leaves 
largely perform this function. 

801. Holdfasts. — These are organs for anchorage which are 
not true roots. These are especially well developed in some of 
the algae (Fucus, Laminaria, etc.). They are usually called 
holdfasts. The holdfasts of the larger algae are mainly for 
anchoring the plant. They do not function as absorbing organs, 
and the structure is different from that of true roots. 

802. Haustoria or suckers is a name applied to another kind 
of holdfast employed by parasitic plants. In the dodder the 
haustorium penetrates the tissue of the host (the plant on which 
the parasite grows), and besides furnishing a means of attach- 
ment, it serves as an absorbing organ by means of which the 
parasite absorbs food from its host. The parasitic fungi like 
the powdery mildews which grow on the surface of their hosts 
have simple haustoria which serve both as organs of attachment 
and absorption, while in the rusts which grow in the interior of 
their hosts the haustoria are merely absorbing organs. 

803. Rootlets, or rhizoids. — Many of the algae, liverworts and 
mosses have slender, hair-like organs of attachment and absorp- 
tion. These plants do not have true roots. Because of the 
slender form and small size of these organs, they are called 
rhizoids, or rootlets. In form many of them resemble the root- 
hairs of higher plants. 






CHAPTER XLIL 

THE FLORAL SHOOT. 

I. The Parts of the Flower. 

The portion of the stem on which the flowers are borne is 
the flower shoot or axis, or taken together with the flowers, it is 
knowr as the Flower Cluster. 

804 > The flower. — The flower is best understood by an exam- 
ination, first of one of the types known as a " complete " flower, 
as in the buttercup, the spring beauty, the bloodroot, the apple, 
the rose, etc. 

There are two sets of organs or members in the complete 
flower — (i) the floral envelope; (2) the essential or necessary 
members or organs. 

The floral envelope when complete consists of — 1st, an outer 
envelope, the calyx, made up of several leaflike structures 
{sepals), very often possessing chlorophyll, which envelop all 
the other parts of the flower when in bud; 2d, an inner envelope, 
the corolla, also made up of several leaflike parts (petals), usu- 
ally bright colored and larger than the sepals. The outer and 
inner floral envelopes are usually in whorls (though in close spirals 
in many of the buttercup family, etc.), and for reasons discussed 
elsewhere (Chapter XXXIV) represent leaves. The essential 
or necessary members of the flower are also usually in whorls 
and likewise represent leaves, but only in rare cases is there any 
suggestion, either in their form or color, of a leaf relationship. 
These members are in two sets: (1) The outer, or andrcecium, 
consisting of a few or many parts (stamens); (2) the inner set, 
the gyncecium, consisting of a few or many parts (carpels). 

419 



420 RELATION TO ENVIRONMENT. 

805. Purpose of the flower. — While the ultimate purpose of all 
plants is the production of seed or its equivalent through which 
the plant gains distribution and perpetuation, the flower is the 
specialized part of the seed plant which utilizes the food and 
energies contributed by other members of the plant organization 
for the production of seed. In addition to this there are definite 
functions performed by the members of the flower, which come 
under the general head of plant work, or flower work. 

806. The calyx, or the sepals. — These are chiefly protective, 
affording protection to the young stamens and carpels in the 
flower bud. Where the corolla is absent, sepals are usually 
present and then assume the function of the petals. In a few 
instances the calyx may possibly ultimately join in the formation 
of the fruit (examples: the butternut, walnut, hickory). 

807. The corolla, or petals. — The petals are partly protective 
in the bud, but their chief function where well developed seems 
to be that of attracting insects, which through their visits to the 
flower aid in "pollination" especially " cross pollination" 

808. The stamens. — The stamens ( = microsporophylls) are 
flower organs for the production of pollen, or pollen-spores 
( = microspores) . The stalk (not always present) is the filament, 
the anther is borne on the filament when the latter is present 
The anther consists of the anther sacs or pollen sacs (microspo- 
rangium) containing the pollen-spores, and the connective, the 
sterile tissue lying between and supporting the anther sac. The 
stamens are usually separate, but sometimes they are united by 
their filaments, or by their anthers. When the pollen is ripe 
they open by slits or pores and the pollen is scattered; or in 
rarer cases the pollen mass (pollinium) is removed through the 
agency of insects (see Insect pollination, Chap. XLIII). 

809. The pistil. — The pistil consists of the "ovary," the style 
(not always present), and the stigma. These are well shown in 
a simple pistil, common examples of which are found in the 
buttercup, marsh marigold, the pea, bean, etc. The simple 
pistil is equivalent to a carpel ( = macrosporophyll), while the 
compound pistil consists of two or several carpels joined, as in 



THE FLORAL SHOOT. 4 21 

the toothwort, trillium, lily, etc. The ovary is the enlarged part 
which below is attached to the receptacle of the flower, and con- 
tains within the ovules. The style, when present, is a slender 
elongation of the upper end of the ovary. The stigma is sup- 
ported on the end of the style when the latter is present. It is 
often on a capitate enlargement of the style or extends down one 
side, or when the style is absent it is usually seated directly on 
the upper end of the ovary. The stigmatic surface is glutinous 
or "sticky," and serves to hold the pollen-spores when they 
come in contact with it. 

The ovules are within the ovary and are arranged in different 
ways in different plants. The pollen-grain (or better pollen- 
spore = microspore), after it has been transferred to the stigma, 
"germinates," and the pollen tube grows down through the 
tissue of the stigma and style, or courses down the stylar canal 
until it reaches the ovule. Here it usually enters the ovule 
(macrosporangium) at the micro pyle (in some of the ament- 
bearing plants it enters at the chalaza), and the sperm- cells are 
emptied into the embryo sac in the interior of the ovule. 

810. Fertilization. — One of the sperms unites with the egg in 
the embryo sac. This is fertilization, and from the fertilized 
egg the young embryo is formed still within the ovule. Double 
fertilization, — the other sperm-cell sometimes unites with one 
or both of the "polar" nuclei which have united to form the 
"definitive" or "endosperm" nucleus. As a result of fertiliza- 
tion, the embryo plant is formed within the ovule, the coats of 
which enlarge by growth forming the seed coats, and altogether 
forming the seed. (See Chapters XXXIV, XXXV, XXXVI.) 



II. Kinds of Flowers. 

811. Absence of certain flower parts. — The complete flower 
contains all the four series of parts. ^Tien any one of the series 
of parts is lacking, the flower is said to be incomplete. Where only 
one series of the floral envelopes is present the flowers are said to 
be apetalous (the petals are absent), examples: elm, buckwheat, 



422 RELATION TO ENVIRONMENT. 

etc. Flowers which lack both floral envelopes are naked. When 
pistils are absent but stamens are present the flowers are stami- 
nate, whether floral envelopes are present or not; and so when 
stamens are absent and pistils present the flower is pistillate. Ii 
both stamens and pistils are absent the flower is said to be sterile 
or neutral (snowball, marginal or showy flowers in hydrangea). 
Flowers with both stamens and pistils, whether or not they have 
floral envelopes, are perfect (or hermaphrodite), so if only one 
of these sets of essential organs of the flower is present the flower 
is imperfect, or diclinous. Sometimes the imperfect, or diclinous, 
flowers are on the same plant, and the plant is said to be monoe- 
cious (of one household). When staminate flowers are on cer- 
tain individual plants, and the pistillate flowers of the same 
species are on other individuals, the plant is dioecious (or of two 
households). When some of the flowers of a plant are diclinous 
and others are perfect, they are said to be polygamous. 

Many of these variations relating to the presence or absence of 
flower parts in one way or another contribute to the well-being 
of the plant. Some indicate a division of labor; thus in the 
neutral flowers of certain species of hydrangea or viburnum, the 
showy petals serve to attract insects which aid in the pollination 
of the fertile flowers. It must not be understood, however, that all 
variations in plants which results in new or different forms of flowers 
is for the good of the species. For example, under cultivation 
the flowers of viburnum and hydrangea sometimes are all neu- 
tral and showy. While such variations sometimes contribute to 
the happiness of man, the plant has lost the power of developing 
seed. In diclinous flowers cross pollination is necessitated. 

812. Form of the flower. — The flower as a whole has form. 
This is so characteristic that in general all flowers of the different 
individuals of a species are of the same shape, though they may 
vary in size. In general, flowers of closely related plants of dif- 
ferent species are of the same type as to form, so that often in the 
shape of the flower alone we can see the relationship of kind, 
though the form of the flower is not the most important nor 
always the sure index of kinship. Since many flowers resemble. 



THE FLORAL SHOOT. 



423 



certain familiar objects, names are often used which relate to 
these objects. 

Flowers are said to be regular, or irregular. In a regular 
flower all of the parts of a set or series are of the same shape and 
size, while in irregular flowers the parts are of a different shape 
or size in some of the sets. The flowers of the pea family (Papi- 
lionacece), of the mint family (Labiatce), of the morning glory, 
larkspur, monkshood, etc., are irregular (fig. 450). The corolla 
usually gives the characteristic form to the flower, and the name 
is usually applied to the form of the corolla. 

Some of the different forms are wheel-shaped or rotate corolla 
when the petals spread out at once like the spokes of a wheel, as 
in the potato, tomato, or bittersweet; salver-shaped when the 




Fig. 450. 
Several forms of flowers. Regular flowers, wh, wheel-shaped corolla; sa, 
salver-shaped; tub, tubular-shaped. Irregular flowers, pa, butterfly or papilio- 
naceous; per, personate or masked flower; lab, gaping or ringent corolla. The 
two latter are called bilabiate flowers. 



petals spread out at right angles from the end of a corolla tube, 
as in the phlox; bell-shaped, or campanulate, as in the harebell 
or campanula; funnel-shaped, as in the morning glory; tubular, 
when the ends of the petals spread but little or none from the 
end of the corolla tube, as in the turnip flower or in the disk 
florets of the composites. The butterfly, or papilionaceous cor- 
olla is peculiar as in the pea or bean. The upper petal is the 
"banner," the two lateral ones the "wings," and the two lower 
the "keel." 

The labiate corolla is charcteristic of the mint family where 
the gamosepalous corolla is unequally divided, so that the twy 



424 RELATION TO ENVIRONMENT. 

upper lobes are sharply separated from the three lower forming 
two "lips." The labiate corolla of the toadflax, or snapdragon 
is personate, or masked, because the lower lip arches upward 
like a palate and closes the entrance to the corolla tube; that of 
the dead nettle (Lamium) is ringent or gaping, because the lips 
are spread wide apart. In some plants the labiate corolla is net 
very marked and differs but slightly from a regular form. 

The ligulate or strap-shaped corolla is characteristic of the 
flowers of the dandelion or chicory, or of the ray flowers of other 
composites (fig. 451). The lower part of the gamosepalous 
corolla is tubular, and the upper part is strap-shaped, as if that 
part of the tube were split on one side and spread out flat. 

These forms of the flower should be studied in appropriate 
examples. 

813. Union of flower parts. — In the buttercup flower all the 
parts of each series are separate from one another and from 
other series of parts. Each one is attached to the receptacle of 
the flower, which is a very much shortened portion of the flower 
axis. The calyx being composed of separate and distinct parts 
is said to be polysepalous, and the corolla is likewise polypetal- 
011s. The stamens are distinct, and the pistils are simple. In 
many flowers, however, there is a greater or lesser union of parts. 

814. Union of parts of the same series or cycle. — The parts 
coalesce, either slightly or to a great extent. Usually they are 
not so completely coalesced but what the number of parts of 
the series can be determined. Where the sepals are united the 
calyx is gamosepalous, when the petals are united the corolla is 
gamopetalous. 

Union of the sepals or of the corolla is quite common, but 
union of the stamens is rare except in a few families where 
it is quite characteristic. When the stamens are united by 
their anthers, they are syngenoesious. This is the case in 
most flowers of the composite family. When all the stamens 
are united into one group by their filaments, they are moua- 
delphous (one brotherhood), as in holy hock, hibiscus, cotton ? 



THE FLORAL SHOOT. 425 

marsh-mallow, etc. When they are united by their filaments in 
two groups, they are diadelphous (two brotherhoods), as in the 
pea and most members of the pea family. In most species of 
St. John's wort (Hypericum), the stamens are united in threes 
(triadelphous). 

815. The carpels are often united. — The pistil is then said to 
be compound. Where the pistils are consolidated, usually the 
adjacent walls coalesce and thus separate the cavity of each 
ovary. Each cavity in the compound pistil is a locule. In 
some cases the adjacent walls disappear so that there is one com- 
mon cavity for the compound pistil (examples: purslane, chick- 
weeds, pinks, etc.). In a few cases there is a false partition 
(example, in the toothwort and other crucifers). The compound 
pistil is very often lobed slightly, so that the different pistils can 
be discerned. More often the styles or stigmas are distinct, and 
thus indicate the number of pistils united. 

816. Union of the parts of different series. — While in the 
buttercup and many other flowers, all the different parts are 
inserted on the torus or receptacle, in other flowers one series of 
parts may be joined to another. This is adnation of parts, or 
the two or more series are adnate. In the morning glory the 
stamens are inserted on the inner face of the corolla tube; the 
same is true in the mint family, and there are many other ex- 
amples. The insertion of parts, whether free or adnate, is usually 
spoken of in reference to their relation to the pistil. Thus, 
in the buttercup the floral envelopes and stamens are all free 
and hypogynons they are below the pistil. The pistil in thi; 
case is superior. In the cherry, pear, etc., the petals and stamen- 
arc borne on the edge of the more or less elevated tube of ihr 
calyx, and arc said to be perigynous, i.e., around the pistil 
In the cranberry, huckleberry, etc.. the calyx is for the most 
part united with the waD of the ovary with the short calyx limbs 
projecting from the upper surface. The petals and stamens 
are inserted on the edge of the calyx above the ovary; they are, 
therefore, epigynous, and the ovary being under the calyx, as 
it were, is inferior. 



426 RELATION TO ENVIRONMENT. 



III. Arrangement of Flowers, or Mode of Inflores- 
cence. 

817. Flowers are solitary or clustered. — Solitary flowers are 
more simple in their arrangement, i.e., it is easier for us to deter- 
mine and name their relation to each other and to other parts 
of the plant. They are either axillary, i.e., on short lateral 
shoots in the axils of ordinary foliage leaves, or they are terminal, 
i.e., they are borne on the end of the main axis of an ordinary 
foliage shoot. In either case they are so far separated, and the 
foliage leaves are so prominent, they do not form recognizable 
groups or clusters. The manner of arrangement of flowers on 
the shoot is called inflorescence, while the group of flowers so 
arranged is the flower cluster. 

Two different modes of inflorescence are usually recognized 
in the arrangement of flowers on the stem, (i) The corymbose, 
or indeterminate inflorescence (also indefinite inflorescence), in 
which the flowers arise from axillary buds, and the terminal bud 
may continue to grow. (2) The cymose or determinate inflor- 
escence (also definite inflorescence) in which the flowers arise 
from terminal buds. This arrests the growth of the shoot in 
length. 

There are several advantages to the plant in the different 
modes of inflorescence, chief among which is the massing of the 
flowers, thus increasing the chances for effective pollination. 

A. FLOWEB CLUSTERS WITH INDETERMINATE INFLORESCENCE. 

818. The simplest mode of indeterminate inflorescence is 

where the flowers arise in the axils of normal foliage leaves, 
while the terminal bud, as in the florist's smilax, the bellwort, 
moneywort, apricot, etc., continues to grow. The flowers are 
solitary and axillary. In other cases which are far more numer- 
ous, the flowers are associated into more or less definite clusters 
in which are a number of recognizable types. The word type 
used in this sense, it should be understood, does not refer to an 



THE FLORAL SHOOT. 427 

original structure which is the source of others. It merely refers 
to a mode of inflorescence which we attempt to recognize, and 
about which we group those forms which have a resemblance to 
one another. There are many forms of flower clusters which 
do not conform to any one of our recognized types, and are very 
puzzling. The evolution of the flower clusters has been natural, 
and we cannot make them all conform to an artificial classifica- 
tion. These types are named merely as a matter of convenience 
in the expression of our ideas. The types usually recognized 
are as follows: 

819. The raceme. — The flower-shoot is more or less elongated, 
and the leaves are reduced to a minute size termed bracts, while 
the flowers on lateral axes are solitary in the axils of the bracts. 
The reduction in the size of the leaves and the somewhat limited 
growth of the shoot in length, makes the flowers more prominent, 
and brings them into closer relation than if they were formed in 
the axils of the leaves on the ordinary foliage shoot. The choke 
cherry, currant, pokeweed, sourwood, etc., are examples of a 
raceme (fig. 569). In most plants with the raceme type, while 
the inflorescence is indeterminate, and the uppermost flowers 
(those toward the end of the main shoot) are younger, still the 
period of flowering is somewhat restricted and the raceme stops 
growing. In a few plants, however, as in the common "shep- 
herd's purse," the raceme continues to grow throughout the 
summer, so that the lower flowers may have ripened their seed 
while the terminal portion of the raceme is still growing and 
producing new flowers. Compound racemes are formed when 
by branching of the flower-shoot there are several racemes in a 
cluster, as in the false Solomon's seal (Smilacina racemosa). 

820. The panicle. — The panicle is developed from the raceme 
type by the branching of the lateral flower-axes forming a loose 
open flower cluster, as in the oat. 

821. The thyrsus is a compact panicle of pyramidal form, as 
in the lilac, horsechestnut, etc. 

822. The corymb. — The corymb shows likewise an easy tran- 
sition from the raceme type, by the shortening of the main axis 



428 RELATION TO ENVIRONMENT. 

of inflorescence, and the lengthening of the lower, lateral flower 
peduncles so that the flower cluster is more or less flattened on 
top. This represents the simple corymb. A compound corymb 
!s one in which some of the flower peduncles branch again form- 
ing secondary corymbs, as in the mountain ash. It is like a 
panicle with the lower flower stalks elongated. 

823. The umbel. — The umbel is developed from the raceme, 
or corymb. The main flower-shoot remains very short or unde- 
veloped with several flowers on long peduncles arising close to- 
gether around this shortened axis, in the form of a whorl or clus- 
ter. Examples are found in the milkweed, water pennywort 
(Hydrocotyle), the oxheart cherry, etc. A compound umbel is 
one in which the peduncles are branched, forming secondary 
umbels, as in the caraway, parsnip, carrot, etc. 

824. The spike. — In the spike the main axis is long, and the 
solitary flowers in the axils of the bracts are usually sessile, and 
often very much crowded. The plaintain, mullein (fig. 422), 
etc., are examples. The spike is a raceme, only the flowers are 
sessile and crowded. In the grasses the flower cluster is branched, 
and the branchlets bearing a few flowers are spikekts. 

825. The head. — When the flower axis is very much short- 
ened and the flowers crowded and sessile or nearly so, forming a 
globose or compressed cluster, it is a head or capiadum. The 
transition is from a spike by the shortening of the main axis, as 
in the clover, button bush (Cephalanthus), etc., or in the short- 
ening of the peduncles in an umbel, as in the daisy, dandelion, 
and other composite flowers. In these the head is surrounded 
by an involucre, which in the young head often envelopes the 
mass of flowers, thus affording them protection. In some other 
composites (Lactuca, for example) the involucre affords pro- 
tection for a longer period, even while the seeds are ripening. 

826. The spadix — When the main axis of the flower cluster 
is fleshy, the spike or head forms a spadix, as in the Indian tur- 
nip, the skunk cabbage, the calla, etc. The spadix is usually 
more or less enclosed in a spathe, a somewhat strap-shaped leaf. 

£27, The catkin.— A spike which is usually caducous, i.e., 



THE FLORAL SHOOT. 



429 



falls away after the maturity of the flower or fruit, is called a 
catkin, or an ament. The flower clusters of the alder, willow, 
(fig. 555), poplar, and the staminate flower clusters of the oak, 
hickory, hazel, birch, etc., are aments. So characteristic is this 




Head of sunflower showing centripetal inflorescence of tubular flowers, 
by the Author.) 



(Photo 



mode of inflorescence that the plants are called amentiferous, or 
amentaceous. 
828. Anthesis of flowers with indeterminate inflorescence. — 

In the anthesis of the raceme as well as in other corymbose forms 
the lower (or outer) flowers being older, open first. The open- 
ing of the flowers then takes place from below, upward; or from 
the outside, inward toward the center of inflorescence. The 
anthesis, i.e., the opening of the flowers of corymbose forms is 
said to be centripetal, i.e., it progresses from outside, inward. 
The anthesis of the fuller's teazel is peculiar, since it shows both 
types. There are several distinct advantages to the plant where 



430 



RELATION TO ENVIRONMENT. 



anthesis extends over a period of time, as it favors cross pollina- 
tion, favors the formation of seed in case conditions should be 




Fig. 452. 
Heads of fuller's teazel in different stages of flowering. 

unfavorable at one period of anthesis, distributes the drain on 
the plant for food, etc. 

B. FLOWER CLUSTERS WITH DETERMINATE INFLORESCENCE. 

829. The simplest mode of determinate inflorescence is a 

plant with a solitary terminal flower, as in the hepatica, the tulip, 
etc. The leaves in these two plants are clustered in the form of a 
rosette, and the aerial shoot is naked and bears the single flower 
at its summit. Such a flower-shoot is a scape. As in the case 
of the indeterminate inflorescence, so here the larger number 
of flower-shoots are more complex and specialized, resulting in 
the evolution of flower clusters or masses. Accompanying the 
association of flowers into clusters there has been a reduction in 
leaf surface on the flower-shoot so that the flowers predominate 
in mass and are more conspicuous. Among the recognized 
modes of determinate inflorescence, the following are the chief 
ones: 

830. The cyme. — In the cyme the terminal flower on the main 
axis opens first and the remaining flowers are borne on lateral 
shoots, which arise from the axils of leaves or bracts, below. 



THE FLORAL SHOOT. 



431 



These lateral shoots usually branch and elongate so that the 
terminal flowers on all the branches reach nearly the same height 
as the terminal flower on the main shoot, forming a somewhat 
flattened or convex top of the flower cluster. This is illustrated 




B C 

Fig. 45 3- 
Diagrams of cymose inflorescence. A, dichasium ; B, scorpioid cyme; C, heli- 
coid cyme. (After Strastmrger. ) 

in the basswood flower. The anthesis of the cyme is centrifugal, 
i.e., from the inside outward to the margin. But it is often more 
or less mixed, since the lateral shoots if they bear more than one 
flower are dimunitive cymes and the terminal flower opens before 
the lateral ones. Where the flower cluster is quite large and 
the branching quite extensive, compound cymes are formed, as 
in the dogwood, hydrangea, etc. 

831. The helicoid cyme. — Where successive lateral branch- 
ing takes place, and always continues on the same side a curved 
flower cluster is formed, as in the forget-me-not and most mem- 
bers of the borage family. This is known as a helicoid cyme 
(fig. 453, C). Each new branch becomes in turn the "false" 
axis bearing a new branch on the same side. 

832. The scorpioid cyme. — A scorpioid cyme (fig. 453, B) is 
formed where each new branch arises on alternate sides of the 
"false" axis. 

833. The forking cyme is where each "false" axis produces 
two branches opposite, so that it represents a false dichotomy 
(example, the flower cluster of chickweed). 

834. Some of these flower clusters are peculiar and it is difn- 



43 2 RELATION TO ENVIRONMENT. 

cult to see how the helicoid, or scorpioid, cymes are of any 
advantage to the plant over a true cyme. The inflorescence of 
the plant being determinate, if the flowering is to be extended 
over a considerable period a peculiar form would necessarily 
result. In the helicoid cyme continued branching takes place 
on one side, and the result in the forget-me-not is a continued 
inflorescence in its effect like that of a continued raceme (com- 
pare shepherd' s-purse). But we should not expect that all 
of the complex and specialized structures from simple and gen- 
eralized ones are beneficial to the plant. In many plants we 
recognize evolution in the direction of advantageous structures. 
But since the plant cannot consciously evolve these structures, 
we must also recognize that there may be phases of retrogression 
in which the structures evolved are not so beneficial to the plant 
as the more simple and generalized ones of its ancestors. Varia- 
tion and change do not result in advancing the plant or plant 
structures merely along the lines which will be beneficial. The 
tendency is in all directions. The result in general may be dia- 
gramed by a tree with divergent and wide-reaching branches. 
Some die out; others remain subordinate or dormant; while 
still others droop downward, showing a retrogression. But in 
this backward evolution they do not return to the condition of 
their ancestors, nor is the same course retraced. A new down- 
ward course is followed just as the downward-growing branch 
follows a course of its own, and does not return in the trunk. 



CHAPTER XLIII. 

POLLIN ATION. 

Origin of heterospory, and the necessity for 
pollination. 

835. Both kind*, of sexual organs on the same prothallium. — In the ferns, as 
we have seen, the sexual organs are borne on the prothallium, a small, leaf-like, 
heart-shaped body growing in moist situations. In a great many cases both 
kinds of sexual organs are borne on the same prothallium. While it is per- 
haps not uncommon, in some species, that the egg cell in an archegonium 
may be fertilized by a spermatozoid from an antheridium on the same pro- 
thallium, it happens many times that it is fertilized by a spermatozoid from 
another prothallium. This may be accomplished in several ways. In the 
first place antheridia are usually found much earlier on the prothallium than 
are the archegonia. When these antheridia are ripe, the spermatozoids es- 
cape before the archegonia on the same prothallium are mature. 

836. Cross fertilization in monoecious prothallia. — By swimming about in 
the water or drops of moisture which are at times present in these moist situa- 
tions, these spermatozoids may reach and fertilize an egg which is ripe 
in an archegonium borne on another and older prothallium. In this way 
what is termed cross fertilization is brought about nearly as effectually as if 
the prothallia were dioecious, i.e. if the antheridia and archegonia were all 
borne on separate prothallia. 

837. Tendency toward dioecious prothallia. — In other cases some fern pro- 
thallia bear chiefly archegonia, while others bear only antheridia. In these 
cases cross fertilization is enforced because of this separation of the sexual 
organs on different prothallia. These different prothallia, the male and 
female, are largely due to a difference in food supply, as has been clearly 
proven by experiment. 

838. The two kinds of sexual organs on different prothallia. — In the horse- 
tails (equisetum) the separation of the sexual organs on different prothallia has 
become quite constant. Although all the spores are alike, so far as we can 
determine, some produce small male plants exclusively, while others produce 

433 



434 RELATION TO ENVIRONMENT. 

large female plants, though in some cases the latter bear also antheridia. It 
has been found that when the spores are given but little nutriment they form 
male prothallia, and the spores supplied with abundant nutriment form 
female prothallia. 

839. Permanent separation of sexes by different amounts of nutriment sup- 
plied the spores. — This separation of the sexual organs of different prothallia, 
which in most of the ferns, and in equisetum, is dependent on the chance 
supply of nutriment to the germinating spores, is made certain when we come 
to such plants as isoetes and selaginella. Here certain of the spores receive 
more nutriment while they are forming than others. In the large sporangia 
(macrosporangia) only a few of the cells of the spore -producing tissue form 
spores, the remaining cells being dissolved to nourish the growing macro- 
spores, which are few in number. In the small sporangia (microsporangia) 
all the cells of the spore-producing tissue form spores. Consequently each 
one has a less amount of nutriment, and it is very much smaller, a micro- 
spore. The sexual nature of the prothallium in selaginella and isoetes, then, is 
predetermined in the spores while they are forming on the sporophyte. The 
microspores are to produce male prothallia, while the macrospores are to 
produce female prothallia. 

840. Heterospory. — This production of two kinds of spores by isoetes, 
selaginella, and some of the other fern plants is heterospory, or such plants 
are said to be heterosporous. Heterospory, then, so far as we know from liv- 
ing forms, has originated in the fern group. In all the higher plants, in the 
gymnosperms and angiosperms, it has been perpetuated, the microspores being 
represented by the pollen, while the macrospores are represented by the em. 
bryo sac; the male organ of the gymnosperms and angiosperms being the 
antherid cell in the pollen or pollen tube, or in some cases perhaps the pollen 
grain itself, and the female organ in the angiosperms perhaps reduced to 
the egg cell of the embryo sac. 

841. In the pteridophytes water serves as the medium for conveying the 
sperm cell to the female organ. — In the ferns and their allies, as well as in 
the liverworts and mosses, surface water is a necessary medium through 
which the generative or sperm cell of the male organ, the spermatozoid, may 
reach the germ cell of the female organ. The sperm cell is here motile. 
This is true in a large number of cases in the algae, which are mostly aquatic 
plants, while in other cases currents of water float the sperm cell to the 
female organ. 

842. In the higher plants a modification of the prothallium is necessary. 
— As we pass to the gymnosperms and angiosperms, however, where the 
primitive phase (the gametophyte) of the plants has become dependent solely 
on the modern phase (the sporophyte) of the plant, surface water no longer 
serves as the medium through which a motile sperm cell reaches the egg cell 
to fertilize it. The female prothallium, or macrospore, is, in nearly all 



POLLINATION. 435 

cases, permanently enclosed within the sporangium, so that if there were 
motile sperm cells on the outside of the ovary, they could never reach the 
egg to fertilize it. 

843. But a modification of the microspore, the pollen tube, enables the 
sperm cell to reach the egg cell. The tube grows through the nucellus, 
or first through the tissues of the ovary, deriving nutriment therefrom. 

844. But here an important consideration should not escape us. The pol- 
len grains (microspores) must in nearly all cases first reach the pistil, in 
order that in the growth of this tube a channel may be formed through which 
the generative cell can make its way to the egg cell. The pollen passes from 
the anther locule, then, to the stigma of the ovary. This process is termed 
pollination. 

Pollination. 

845. Self pollination, or close pollination. — Perhaps very few of the ad- 
mirers of the pretty blue violet have ever noticed that there are other flowers 
than those which appeal to us through the beautiful colors of the petals. 
How many have observed that the brightly colored flowers of the blue violet 
rarely " set fruit" ? Underneath the soil or debris at the foot of the plant 
are smaller flowers on shorter, curved stalks, which do not open. When the 
anthers dehisce, they are lying close upon the stigma of the ovary, and the 
pollen is deposited directly upon the stigma of the same flower. This 
method of pollination is self pollination, or close pollination. These small, 
closed flowers of the violet have been termed " cleisiogamous" because they 
are pollinated while the flower is closed, and fertilization takes place as a 
result. 

But self pollination takes place in the case of some open flowers. In some 
cases it takes place by chance, and in other cases by such movements of the 
stamens, or of the flower at the time of the dehiscence of the pollen, that it 
is quite certainly deposited upon the stigma of the same flower. 

846. Wind pollination. — The pine is an example of wind-pollinated flowers. 
Since the pollen floats in the air or is carried by the "wind," such flowers are 
anemophilons . Other anemophilous flowers are found in other conifers, in 
grasses, sedges, many of the ament-bearing trees, and other dicotyledons. 
Such plants produce an abundance of pollen and always in the form of 
"dust," so that the particles readily separate and are borne on the wind. 

847. Pollination by insects. — A large number of the plants which we have 
noted as being anemophilous are monoecious or dioecious, i.e. the stamens 
and pistils are borne in separate flowers. The two kinds of flowers thus formed, 
the male and the female, are borne either on the same individual (monoe- 
cious) or on different individuals (dioecious). In such cases cross pollination. 



43^ 



RELATION TO ENVIRONMENT. 



i.e. the pollination of the pistil of one flower by pollen from another, is 
sure to take place, if it is pollinated at all. Even in monoecious plants cross 
pollination often takes place between flowers of different individuals, so that 




Fig. 454- 
Viola cucullata ; blue flowers above, cleistogamous flowers smaller and curved below. 
Section of pistil atjright. 

more widely different stocks are united in the fertilized egg, and the strain 
is kept more vigorous than if very close or identical strains were united. 

848. But there are many flowers in which both stamens and pistils are pres- 
ent, and yet in which cross pollination is accomplished through the agency oJ 
insects. 

859. Pollination of the bluet. — In the pretty bluet the stamens and 
styles of the flowers are of different length as shown in figures 455, 4-6. 
The stamens of the long-styled flower are at about the same level as the 
stigma of the short-styled flower, while the stamens of the latter are on 



POLLINA TION. 



437 



about the same level as the stigma of the former. What does this interesting 
relation of the stamens and pistils in the two different flowers mean ? As the 
butterfly thrusts its "tongue" down into the tube of the long-styled flower 





Fig. 45 :• 

Dichogamous flower of the bluet (Houstonia ccerulea), the long-styled form. 



for the nectar, some of the pollen will be rubbed off and adhere to it. When 
now the butterfly visits a short-styled flower this pollen will be in the right 
position to be rubbed off onto the stigma of the short style. The positions of 





Fig. 456. 
Dichogamous flower of bluet (Houstonia cceruL-aj, the short-styled form. 

the long stamens and long style are such that a similar cross pollination will 
be effected. 

850. Pollination of the primrose. — In the primroses, of which we have 
examples growing in conservatories, that blossom during the winter, we 
have almost identical examples of the beautiful adaptations for cross polli- 
nation by insects found in the bluet. The general shape of the corolla is 



438 



RELATION TO ENVIRONMENT 



the same, but the parts of the flower are in fives, instead of in fours as in 
the bluet. While the pollen of the short-styled primulas sometimes must 
fall on the stigma of the same flower, Darwin has found that such pollen is 




Fig. 457- 
Dichogamous flowers of primula. 



not so potent on the stigma of its own flower as on that of another, an ad- 
ditional provision which tends to necessitate cross pollination. 

In the case of some varieties of pear trees, as the bartlett, it has been 
found that the flowers remain largely sterile not only to their own pollen, or 
pollen of the flowers on the same tree, but to all flowers of that variety. 
However, they become fertile if cross pollinated from a different variety of 
pear. 

851. Pollination of the skunk's cabbage. — In many other flowers cross 
pollination is brought about through the agency of insects, where there is a 
difference in time of the maturing of the stamens and pistils of the same 
flower. The skunk's cabbage (Spathyema fcetida), though repulsive on 
account of its fetid odor, is nevertheless a very interesting plant to study for 
several reasons. Early in the spring, before the leaves appear, and in many 
cases as soon as the frost is out of the hard ground, the hooked beak of the 
large fleshy spathe of this plant pushes its way through the soil. 

If we cut away one side of the spathe as shown in fig. 459 we shall have 
the flowering spadix brought closely to view. In this spadix the pistil of 
each crowded flower has pushed its style through between the plates of 
armor formed by the converging ends of the sepals, and stands out alone 
with the brush-like stigma ready for pollination, while the stamens of all the 
flowers of this spadix are yet hidden beneath. The insects which pass from 
the spadix of one plant to another will, in crawling over the projecting 
stigmas, rub off some of the pollen which has been caught while visiting a 
plant where the stamens are scattering their pollen. In this way cross pollin 
ation is brought about. Such flowers, in which the stigma is prepared 



POLLINA TION. 



439 




Fig. 45 8. 
Skunk's cabbage. 




Fig. 459. 
Proterogyny in skunk's cabbage. ^Photograph by the author.) 44 ° 



POLLINA TION. 



441 



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life. 


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In ^ 
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H*^EH 

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_.'r 


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■MStRmj 





Fig. 460. 
Skunk's cabbage ; upper flowers proterandrous, lower ones proterogynous. 



44 2 RELATION TO ENVIRONMENT. 

for pollination before the anthers of the same flower are ripe, are proter- 
ogynous. 

852. Now if we observe the spadix of another plant we may see a condi- 
tion of things similar to that shown in fig. 460. In the flowers in the upper 
part of the spadix here the anthers are wedging their way through between 
the armor-like plates formed by the sepals, while the styles of the same 
flowers are still beneath, and the stigmas are not ready for pollination. Such 
flowers are proterandrous, that is, the anthers are ripe before the stigmas of 
the same flowers are ready for pollination. In this spadix the upper flowers 
are proterandrous, while the lower ones are proterogynous, so that it might 
happen here that the lower flowers would be pollinated by the pollen falling 
on them from the stamens of the upper flowers. This would be cross pol- 
lination so far as the flowers are concerned, but not so far as the plants are 
concerned. In some individuals, however, we find all the flowers proter- 
androus. 

853 Spiders have discovered this curious relation of the flowers and in- 
sects. — On several different occasions, while studying the adaptations of the 
flowers of the skunk's cabbage for cross pollination, I was interested to find 
that the spiders long ago had discovered something of the kind, for tney 
spread their nets here to catch the unwary but useful insects. I have not 
seen the net spread over the opening in the spathe, but it is spread over the 
spadix within, reaching from tip to tip of either the stigmas, or stamens, or 
both. Behind the spadix crouches the spider-trapper. The insect crawls 
over the edge of the spadix, and plunges unsuspectingly into the dimly 
lighted chamber below, where it becomes entangled in the meshes of the 
net. 

Flowers in which the ripening of the anthers and maturing of the stigmas 
occur at different times are also said to be dichogamous. 

854 Pollination of jack-in-the-pulpit. — The jack-in-the-pulpit (Arissema 
triphyllum) has made greater advance in the art of enforcing cross pollina- 
tion. The larger number of plants here are, as we have found, dioecious, the 
staminate flowers being on the spadix of one plant, while the pistillate flowers 
are on the spadix of another. In a few plants, however, we find both 
female and male flowers on the same spadix. 

855, The pretty bellflower (Campanula rotundifolia) is dichogamous 
and proterandrous (fig. 462). Many of the composites are also dichoga- 
mous. 

856. Pollination of orchids. — But some of the most marvellous adaptations 
for cross pollination by insects are found in the orchids, or members of the 
orchis family. The larger number of the members of this family grow in the 
tropics. Many of these in the forests are supported in lofty trees where they 
are brought near the sunlight, and such are called "epiphytes." A number 
of species of orchids are distributed in temperate regions. 



POLLINA TION. 



443 



857. Cypripedium, or lady-slipper. — One species of the lady-slipper is 
shown in fig. 468. The labellum in this genus is shaped like a shoe, as one 





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J»l£> 


^K*^^3*3h1 


r^^®w ~'^ • 


• ■ 


^Bl^^ZT^ 






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— . ,**-•:»?..., ^™ 



Fig. 461. 
A group of jacks. 



can see by the section of the flower in fig. 468. The stigma is situated at st t 
while the anther is situated at «, upon the style. The insect enters about 
the middle of the boat-shaped labellum. In going out it passes up and out 



444 



RELATION TO ENVIRONMENT. 



at the end near the flower stalk. In doing this it passes the stigma first and 
the anther last, rubbing against both. The pollen caught on the head of 








Fig. 462. 

Proterandry in the bell-flower (campanula). Left figure shows the syngencecious stamens 
surrounding the immature style and stigma. Middle figure shows the immature stigma being 
pushed through the tube and brushing out the pollen ; while in the right-hand figure, after 
the pollen has disappeared, the lobes of the stigma open out toreceive pollen from another 
flower. 

the insect, will not touch the stigma of the same flower, but will be in posi- 
tion to come in contact with the stigma of the next flower visited. 

858 Epipactis. — In epipactis, shown in fig. 469, the action is similar to 
that of the blue iris. 




Fig. 463- 

Kalmia latifolia, showing position of anthers before insect visits, and at the right the 
scattering of the pollen when disturbed by insects. Middle figure section of flower. 

849. In some of the tropical orchids the pollinia are set free when the insect 
touches a certain part of the flower, and are thrown in such a way that the 
disk of the pollinium strikes the insect's head and stands upright. By the 
time the insect reaches another flower the pollinium has bent downward suffi- 



POLLINA TION. 



445 



ciently to strike against the stigma when the insect alights on the labellum. 
In the mountains of North Carolina I have seen a beautiful little orchid, in 
which, if one touches a certain part ©f the flower with a lead-pencil or other 
suitable object, the pollinium is set free suddenly, turns a complete somer- 
sault in the air, and lands with the disk sticking to the pencil. Many of the 




Spray of leaves and flowers 
of cytisus. 



orchids grown in conservatories can be used to demonstrate some of these 
peculiar mechanisms. 

860. Pollination of the canna. — In the study of some of the marvellous 
adaptations of flowers for cross pollination one is led to inquire if, after all, 
plants are not intelligent beings, instead of mere automatons which respond 





Fig. 46s 
Flower of cytisus grown in conservatory. Same flower scattering poller. 



to various sorts of stimuli. No plant has puzzled me so much in this respect 
as the canna, and any one will be well repaid for a study of recently opened 
flowers, even though it may be necessary to rise early in the morning to 
unravel the mystery, before bees or the wind have irritated the labellum. 
The canna flower is a bewildering maze of petals and petal-like members. 



446 



RELATION TO ENVIRONMENT. 



The calyx is green, adherent to the ovary, and the limb divides into three, 
lanceolate lobes. The petals are obovate and spreading, while the stamens 
have all changed to petal-like members, called staminodia. Only one still 
shows its stamen origin, since the anther is seen at one side, while the fila- 
ment is expanded laterally and upwards to form the staminodium. 










Fig. 466. 
Spartium, showing the dusting of the pollen through the opening keels on the under side 
of an insect. (From Kerner and Oliver.) 

861, The ovary has three locules, and the three styles are usually united 
into a long, thin, strap-shaped style, as seen in the figure, though in some 
cases three, nearly distinct, filamentous styles are present. The end of this 
strap-shaped style has a peculiar curve on one side, the outline being some- 



POLLINA TION. 



447 



times like a long narrow letter S. It is on the end of this style, and along 
the crest of this curve, that the stigmatic surface lies, so that the pollen 




Fig. 468. 
Section of flower of cypripedium. sf, 
stigma ; a, at the left stamen. The insect 
enters the labellum at the center, passes 
under and against the stigma, and out 
through the opening b, where it rubs 
against the pollen. In passing through 
another flower this pollen is rubbed off 
on the stigma. 

must be deposited on the stigmatic end or margin 
in order that fertilization may take place. 

862. If we open carefully canna-flower buds 
which are nearly ready to open naturally, by 
unwrapping the folded petals and staminodia, we shall see the anther-bearing 



Fig. 467. 
Cypripedium. 




Fig. 46g. 
Epipactis with portion of perianth removed to show details. /, labellum ; sf, stigma ; r, 
rostellum; /, pollinium. When the insect approaches the flower its head strikes the disk 
of the pollinium and pulls the pollinium out. At this time the pollinium stands up out of the 
way of the stigma. By the time the insect moves to another flower the pollinia have moved 
downward so that they are in position to strike the stigma and leave the pollen. At the 
right is the head of a bee, with two pollinia (a I attached. 



448 



RELATION TO ENVIRONMENT, 



staminodium is so wrapped around the flattened style that the anther lies 

closely pressed against the face of the style, near the margin opposite that 

on which the stigma lies. 

863. The walls of the anther locules which lie against the style become 

changed to a sticky substance for their entire length, so that they cling 

firmly to the surface of the style 
and also to the mass of pollen 
within the locules. The result is 
that when the flower opens, and 
this staminodium unwraps itself 
from the embrace of the style, the 
mass of pollen is left there de- 
posited, while the empty anther is 
turned around to one side. 

668. Why does the flower de- 
posit its own pollen on the style ? 
Some have regarded this as the act 
of pollination, and have concluded, 
therefore, that cannas are neces- 
sarily self pollinated, and that 
cross pollination does not take 
place. But why is there such evi- 
dent care to deposit the pollen on 

Fig. 47°* the side of the style away from the 

Canna flowers with the perianth removed to .. .. . ., Tf . . ., . 

show the depositing of the pollen on the style by stigmatic margin ? If we visit the 
the stamen. cannas some morning, when a 

number of the flowers have just opened, and the bumblebees are humming 
around seeking for nectar, we may be able to unlock the secret. 

864. We see that in a recently opened canna flower, the petal which 
directly faces the style in front stands upward quite close to it, so that the 
flower now is somewhat funnelshaped. This front petal is the labellum, and 
is the landing place for the bumblebee as he alights on the flower. Here 
he comes humming along and alights on the labellum with his head so close 
to the style that it touches it. But just the instant that the bee attempts to 
crowd down in the flower the labellum suddenly bends downward, as shown 
in fig. 468. In so doing the head of the bumblebee scrapes against the 
pollen, bearing some of it off. Now while the bee is sipping the nectar it is 
too far below the stigma to deposit any pollen on the latter. When the bum- 
blebee flies to another newly opened flower, as it alights, some of the pollen 
of the former flower is brushed on the stigma. 

865. One can easily demonstrate the sensitiveness of the labellum of 
recently opened canna flowers, if the labellum has not already moved down 
in response to some stimulus. Take a lead-pencil, or a knife blade, or even 




POLLINA TION. 



449 



the finger, and touch the upper surface of the labellum by thrusting it 
between the latter and the style. The labellum curves quickly downward. 

866. Sometimes the bumblebees, after sipping the nectar, will crawl up 
over the style in a blundering manner. In this way the flower may be pol- 




'--vK 







Fig. 47i. 
Pollination of the canna flower by bumblebee. 



Canna flower. Pollen on style, sta- 
men at left. 



linated with its own pollen, which is equivalent to self pollination. Un- 
doubtedly self pollination does take place often in flowers which are adapted, 
to a greater or less degree, for cross pollination by insects. 



CHAPTER XLIV. 

THE FRUIT. 

I. Parts of the Fruit. 

867. After the flower comes the fruit. — With the perfection of 
the fruit the seed is usually formed. This is the end towards 
which the energies of the plant have been directed. While the 
seed consists only of the ripened ovule and the contained em- 
bryo, the fruit consists of the ripened ovary in addition, and in 
many cases with other accessory parts, as calyx, receptacle, etc., 
combined with it. The wall of the ripened ovary is called a 
pericarp, and the walls of the ovary form the walls of the fruit. 

868. Pericarp, endocarp, exocarp, etc. — This is the part of 
the fruit which envelops the seed and may consist of the carpels 
alone, or of the carpels and the adherent part of the receptacle, 
or calyx. In many fruits the pericarp shows a differentiation 
into layers, or zones of tissue, as in the cherry, peach, plum, etc. 
The outer, which is here soft and fleshy, is exocarp, while the 
inner, which is hard, is the endocarp. An intermediate layer is 
sometimes recognized and is called mesocarp. In such cases 
the skin of the fruit is recognized as the epicarp. Epicarp and 
mesocarp are more often taken together as exocarp. 

In general fruits are dry or fleshy. Dry fruits may be 
grouped under two heads. Those which open at maturity and 
scatter the seed are dehiscent. Those which do not open are 
indehiscent. 

45o 



THE FRUIT. 



451 



II. Indehiscent Fruits. 




Fig. 472. 

Seed, or akene, 

of buttercup. 



869. The akene. — The thin dry wall of the ovary encloses 
the single seed. It usually does not open and free the seed 
within. Such a fruit is an akene. An akene is 

a dry, indehiscent fruit. All of the crowded but 
separate pistils in the buttercup flower when ripe 
make a head of akenes, which form the fruit of 
the buttercup. Other examples of akenes are 
found in other members of the buttercup family, 
also in the composites, etc. The sunflower seed 
is a good example of an akene. 

870. The samara. — The winged fruits of the maple (fig. 574), 
elm, etc., are indehiscent fruits. They are sometimes called 

key fruits. 

871. The caryopsis is a dry 
fruit in which the seed is con- 
solidated with the wall of the 
ovary, as in the wheat, corn, 
and other grasses. 



872. The schizocarp is a 

dry fruit consisting of several 
locules (from a syncarpons 
gyncecium). At maturity the 




Fig. 473. 
Fruit of red oak. An acorn. 



carpels separate from each other, but do not themselves dehisce 
and free the seed, as in the carrot family, mallow family. 

873. The acorn. — The acorn fruit consists of the acorn and 
the "cup" at the base in which the acorn sits. The cup is a 
curious structure, and is supposed to be composed of an involucre 
of numerous small leaves at the base of the pistillate flower, 
which become consolidated into a hard cup-shaped body. When 
the acorn is ripe it easily separates from the cup, but the hard 
pericarp forming the "shell" of the acorn remains closed. Frost 
may cause it to crack, but very often the pericarp is split open at 
the smaller end by wedge-like pressure exerted by the emerging 
radicle during germination. 



45 2 RELATION TO ENVIRONMENT, 

874. The hazelnut, chestnut, and beechnut. — In these fruits a 
crown of leaves (involucre) at the base of the flower grows around 




Fig. 474- 
Germinating acorn of white oak. 

the nut and completely envelops it, forming the husk or burr. 
When the fruit is ripe the nut is easily shelled out from the husk. 
In the beechnut and chestnut the burr dehisces as it dries and 
allows the nut to drop out. But the fruit is not dehiscent, since 
the pericarp is still intact and encloses the seed. 

875. The hickory-nut, walnut, and butternut. — In these fruits 
the "shuck" of the hickory-nut and the "hull" of the walnut 
and butternut are different from the involucre of the acorn or 
hazelnut, etc. In the hickory-nut the "shuck" probably con- 
sists partly of calyx and partly of involucral bracts consolidated, 
probably the calyx part predominating. This part of the fruit 
splits open as it dries and frees the "nut," the pericarp being 
very hard and indehiscent. In the walnut and butternut the 
"hull" is probably of like origin as the "shuck" of the hickory 
nut, but it does not split open as it ripens. It remains fleshy. 
The walnut and butternut are often called drupes or stone fruits, 
but the fleshy part of the fruit is not of the same origin as the 
fleshy part of the true drupes, like the cherry, peach, plum, etc. 

III. Dehiscent Fruits. 

876. Of the dehiscent fruits several prominent types are rec- 
ognized, and in general they are sometimes called pods. There 
is a single carpel (simple pistil), and the pericarp is dry (gynce- 



THE FRUIT. 



453 



w *~^ cTT Seotifragal 



cium apocarpous) ; or where there are several carpels united the 
pistil is compound (gyncecium syncarpous). 

877. The capsule. — When the capsule is syncarpous it may 
dehisce in three different ways: ist. When the carpels split 
along the line of their union 
with each other longitudi 
nally {septicidal dehiscence). 

as in the azalea or rhodo- ^t^ ^S^ ~~" SepMmgai 

dendron. 2d. When the Fig. 475. 

7 ., Diagrams illustrating three types (m cross- 

Carpels Split down the Mid- section) of the dehiscence of dry fruits. Loc, 
F ^ T . . 7 7 7 7 . loculicidal; Sep, Septicidal, Septifragal. 

die line {loculicidal dehis- 
cence), as in the fruit of the iris, lily, etc. 3d. When the carpels 
open by pores {poricidal dehiscence), as in the poppy. Some 
syncarpous capsules have but one locule, the partitions between 
the different locules when young having disappeared. The 
"bouncing-bet" is an example, and the seeds are attached to a 
central column in four rows corresponding to the four locules 
present in the young stage. 

878. A follicle is a capsule with a single carpel which splits 
open along the ventral or upper suture, as in the larkspur, peony. 

879. The legume, or true pod, is a capsule with a single carpel 
which splits along both sutures, as the pea, bean, etc. As the pod 

ripens and dries, a strong twisting ten- 
sion is often produced, which splits the 
pod suddenly, scattering the seeds. 

880. The silique. — In the toothwort, 
shepherd' s-purse, and nearly all of the 
plants in the mustard family the fruit 
consists of two united carpels, which 
separate at maturity, leaving the par- 
tition wall persistent. Such a fruit is 
a silique; when short it is a silicle, or 
pouch. 

881. A pyxidium, or pyxis, is a cap- 
sule which opens with a lid, as in the 

Fig. 476. plantain. 

Fruit of sweet pea; a pod. r 




454 



RELATION TO ENVIRONMENT. 



IV. Fleshy and Juicy Fruits. 

882. The drupe, or stone-fruit.— In the plum, cherry, peach, 
apricot, etc., the outer portion (exocarp) of the pericarp (ovary) 
becomes fleshy, while the inner portion (endocarp) becomes hard 
and stony, and encloses the seed, or "pit." Such a fruit is known 
as a drupe, or as a stone-fruit. In the almond the fleshy part 
of the fruit is removed. 

883. The raspberry and blackberry.— While these fruits are 




Fig. 477- 
Drupe, or stone-fruit, of plum. 



known popularly as "berries," they are not berries in the tech- 
nical sense. Each ovary, or pericarp, in the flower forms a single 
small fruit, the outer portion being fleshy and the inner stony, just 
as in the cherry or plum. It is a drupelet (little drupe). All of 
the drupelets together make the "berry," and as they ripen the 
separate drupelets cohere more or less. It is a collection, or 
aggregation, of fruits, and consequently they are sometimes called 
collective fruits, or aggregate fruits. In the raspberry the fruit 
separates from the receptacle, leaving the latter on the stem, 
while the drupelets of the blackberry and dewberry adhere to 
the receptacle and the latter separates from the stem. 



THE FRUIT. 



455 



884. The berry. — In the true berry both exocarp (including 
mesocarp) and endocarp are fleshy or juicy. Good examples 
are found in cranberries, huckleberries, gooseberries, currants, 
snowberries, tomatoes, etc. The calyx and wall of the pistil 
are adnate, and in fruit become fleshy so that the seeds are im- 
bedded in the pulpy juice. The seeds themselves are more or 
less stony. In the case of berries, as well as in strawberries, rasp- 
berries, and blackberries, the fruits are eagerly sought by birds 
and other animals for food. The seeds being hard are not 
digested, but are passed with the other animal excrement and 
thus gain dispersal. 

V. Reinforced, or Accessory, Fruits. 

When the torus (receptacle) is grown to the pericarp in fruit, 
the fruit is said to be reinforced. The torus may enclose the 
pericarps, or the latter may be seated upon the torus. 

885. In the strawberry the receptacle of the flower becomes 




Fig. 478. 
Fruit of raspberry. 



larger and fleshy, while the "seeds," which are akenes, are sunk 
in the surface and are hard and stony. The strawberry thus 



45^ RELATION TO ENVIRONMENT. 

differs from the raspberry and blackberry, but like them it is 
not a true berry. 

886. The apple, pear, quince, etc.— In the flower the calyx, 
corolla, and stamens are perigynous, i.e., they are seated on the 
margin of the receptacle, or torus, which is elevated around the 
pistils. In fruit the receptacle becomes consolidated with the 
wall of the ovary (with the pericarp). The torus thus rein- 
forces the pericarp. The torus and outer portion of the pericarp 
become fleshy, while the inner portion of the pericarp becomes 
papery and forms the "core." The calyx persists on the free 
end of the fruit. Such a fruit is called a pome. The receptacle, 
or torus, of the rose-flower, closely related to the apple, is in- 
structive when used in comparison. The rose-fruit is called a 
"hip." 

887. The pepo. — The fruit of the squash, pumpkin, cucum- 
ber, etc., is called a pepo. The outer part of the fruit is the recep- 
tacle (or torus), which is consolidated with the outer part of the 
three-loculed ovary. The calyx, which, with the corolla and 
stamens, was epigynous, falls off from the young fruit. 

VI. Fruits of Gymnosperms. 

The fruits of the gymnosperms differ from nearly all of the 
ang-io sperms in that the seed formed from the ripened ovule is 
naked from the first, i.e., the ovary, or carpel, does not enclose 
the seed. 

888. The cone-fruit is the most prominent fruit of the gymno- 
sperms, as can be seen in the cones of various species of pine, 
spruce, balsam, etc. 

889. Fleshy fruits of the gymnosperms. — Some of the fleshy 
fruits resemble the stone-fruits and berries of the angiosperms. 
The cedar "berries," for example, are fleshy and contain several 
seeds. But the fleshy part of the fruit is formed, not from peri- 
carp, since there is no pericarp, but from the outer portion of 
the ovules, while the inner walls of the ovules form the hard 
Stone surrounding the endosperm and embryo. An examination 



THE FRUIT. 457 

of the pistillate flower of the cedar (juniper) shows usually three 
flask-shaped ovules on the end of a fertile shoot subtended by as 
many bracts (carpels?). The young ovules are free, but as they 
grow they coalesce, and the outer walls become fleshy, forming 
a berry-like fruit with a three-rayed crevice at the apex marking 
the number of ovules. The red fleshy fruit of the yew (taxus) 
resembles a drupe which is open at the apex. The stony seed 
is formed from the single ovule on the fertile shoot, while the red 
cup-shaped fleshy part is formed from the outer integument of 
the ovule. The so-called "aril" of the young ovule is a rudi- 
mentary outer integument. 

The fruit of the maidenhair tree (ginkgo) is about the size of 
a plum and resembles very closely a stone-fruit. But it is merely 
a ripened ovule, the outer layer becoming fleshy while the inner 
layer becomes stony and forms the pit which encloses the em- 
bryo and endosperm. The so-called "aril," or "collar," at the 
base of the fruit is the rudimentary carpel, which sometimes is 
more or less completely expanded into a true leaf. The fruit 
of cycas is similar to that of ginkgo, but there is no collar at the 
base. In zamia the fruit is more like a cone, the seeds being 
formed, however, on the under sides of the scales. 

VII. The "Fruit" of Ferns, Mosses, etc. 

890. The term " fruit " is often applied in a general or popu- 
lar sense to the groups of spore-producing bodies of ferns (jriiit- 
dots, or sori), the spore-capsules of mosses and liverworts, and 
also to the fruit-bodies, or spore-bearing parts, of the fungi and 
algae. 



CHAPTER XLV. 



SEED DISPERSAL. 



891. Means for dissemination of seeds. — During late summer or autumn 
a walk in the woods or afield often convinces us of the perfection and variety 
of means with which plants are provided for the dissemination of their 
seeds, especially when we discover that several hundred seeds or fruits of 
different plants are stealing a ride at our expense and annoyance. The hooks 
and barbs on various seed-pods catch into the hairs of passing animals and 
the seeds may thus be transported 
considerable distances. Among the 
plants familiar to us, which have such 
contrivances for unlawfully gaining 
transportation, are the beggar-ticks 
or stick tights, or sometimes called 





Fig. 479. 
Bur of bidens or bur-marigold, show- 
ing barbed seeds. 



Fig. 480. 
Seed pod of tick-treefoil (desmodium) ; at the 
right some of the hooks greatly magnified. 



bur-marigold (bidens), the tick-treefoil (desmodium), or cockle-bur (xanthi- 
um), and burdock (arctium). 

892. Other plants like some of the sedges, etc., living on the margins of 
streams and of lakes, have seeds which are provided with floats. The wind 
or the flowing of the water transports them often to distant points. 

458 



SEED DISPERSAL. 



459 



893. Many plants pos:ess attractive devices, and offer a substantial 
reward, as a price for the distribution of their seeds. Fruits and berries are 
devoured by birds and other animals ; the seeds within, often passing un- 
harmed, may be carried long distances. Starchy and albuminous seeds and 





Fig. 481. 
Seeds of geum showing the hooklets where the end of the style is kneed. 



grains are also devoured, and while many such seeds are destroyed, others 
are not injured, and finally are lodged in suitable places for growth, often 
remote from the original locality. Thus animals willingly or unwillingly 
become agents in the dissemination of plants over the earth. Man in the 
development of commerce is often responsible for the wide distribution of 
harmful as well as beneficial species. 

894. Other plants are more independent, and mechanisms are employed 
for violently ejecting seeds from the pod or fruit. The unequal tension of 
the pods of the common vetch (Vicia sativa) when drying causes the valves 
to contract unequally, and on a dry summer day the valves twist and pull in 
opposite directions until they suddenly snap apart, and the seeds are thrown 
forcibly for some distance. In the impatiens, or touch-me-not as it is better 
known, when the pods are ripe, often the least touch, or a pinch, or jar, sets 
the five valves free, they coil up suddenly, and the small seeds are thrown 
for several yards in all directions. During autumn, on dry days, the pods 
of the witch hazel contract unequally, and the valves are suddenly spread 
apart, and the seeds are hurled away. 

Other plants have seeds provided with tufts of pappus, or hair-like 
masses, or wing-like outgrowths which serve to buoy them up as they 



460 



RELATION TO ENVIRONMENT. 



are whirled along, often miles away. In late spring or early summer 
the pods of the willow burst open, exposing the seeds, each with a tuft 
of white hairs making a mass of soft down. As the delicate hairs dry, 




Fig. 482. 
Touch-me-not (Impatiens fulva) ; side and front view of flower below ; above unopened 
pod, and opening to scatter the seed. 

they straighten out in a loose spreading tuft, which frees the individual seeds 
from the compact mass. Here they are caught by currents of air and float 
off singly or in small clouds. 

895. The prickly lettuce. — In late summer or early autumn the seeds of 
the prickly lettuce (Lactuca scariola) are caught up from the roadsides by 
the winds, and carried to fields where they are unbidden as well as unwel- 
come guests. This plant is shown in fig. 483. 

896. The wild lettuce. — A related species, the wild lettuce (Lactuca cana- 
densis) occurs on roadsides and in the borders of fields, and is about one 
meter in height. The heads of small yellow or purple flowers are arranged 
in a loose or branching panicle. The flowers are rather inconspicuous, the 
rays projecting but little above the apex of the enveloping involucral bracts, 
which closely press together, forming a flower-head more or less flask- 
shaped. 

At the time of flowering the involucral bracts spread somewhat at the 
apex, and the tips of the flowers are a little more prominent. As the flowers 
then wither, the bracts press closely together again and the head is closed. 
As the seeds ripen the bracts die, and in drying bend outward and down- 
ward, around the flower stem below, or they fall away. The seeds are 



SEED DISPERSAL. 



4 6i 



thus exposed. The dark brown achenes stand over the surface of the recep- 
tacle, each one tipped with the long slender beak of the ovary. The u pap- 
pus," which is so abundant in many of the plants belonging to the composite 
family, forms here a 
pencil-like tuft at the (,f£ ^ 

tip of this long beak. M*M^j 

As the involucral bracts 
dry and curve down- 
ward, the pappus also 
dries, and in doing so 
bends downward and 
stands outward, brist- 
ling like the spokes of 
a small wheel. It is an 
interesting coincidence 
that this takes place 
simultaneously with 
the pappus of all the 
seeds of a head, so 
that the ends of the 
pappus bristles of ad- 
joining seeds meet, 
forming a many-sided 
dome of a delicate and 
beautiful texture. This 
causes the beaks of the 
achenes to be crowded 
apart, and with the 
leverage thus brought to 
bear upon the achenes 
they are pried off the 
receptacle. They are 
thus in a position to 
be wafted away by the 
gentlest zephyr, and 
they go sailing away 
on the wind like a 
miniature parachute. 
As they come slowly 
to the ground the seed 
is thus carefully low- 
ered first, so that it touches the ground in a position for the end which 
contains the root of the embryo to come in contact with the soil. 




Fig. 483- 
Lactuca scariola. 



462 



RELATION- TO ENVIRONMENT. 



897. The milkweed, or silkweed. — The common milkweed, or silkweed 
(Asclepias cornuti), so abundant in rich grounds, is attractive not only 



WE^^ W^K^m 






mpR\ ; -- ^m 




^^s^ '^^B 


J£r ' * 4^ 




'^•jSshH 


mi 9 ■ ^^mm 




'■9 




,iWaH 




JBI 




&.- - * r &/ 




^ *S^HBdw 


m ■:$£>«* •*' %-'.. '•:•;' 8 




#■' # ^ *. '351 


IttLv ' \ 




# # ^teiMl 


flUBST" l ^i' J * ^b«v» '• 4 T 


> 


€ a * c^lySfll Hu 


■!&•••'- ^^fibtti 






I - U 







Fig. 484. 
Milkweed (Asclepias cornuti) ; dissemination of seed. 



because of the peculiar pendent flower clusters, but also for the beautiful 
floats with which it sends its seeds skyward, during a puff of wind, to finally 
lodge on the earth. 

898. The large boat-shaped, tapering pods, in late autumn, are packed 
with oval, flattened, brownish seeds, which overlap each other in rows like 
shingles on a roof. These make a pretty picture as the pod in drying splits 
along the suture on the convex side, and exposes them to view. The silky 
tufts of numerous long, delicate white hairs on the inner end of each seed, 
in drying, bristle out, and thus lift the seeds out of their enclosure, where 
they are caught by the breeze and borne away often to a great distance, 
where they will germinate if conditions become favorable, and take their 
places as contestants in the battle for existence. 

899. The virgin's hower. — The virgin's bower (Clematis virginiana), too, 
clambering over fence and shrub, makes a show of having transformed its 



SEED DISPERSAL. 



463 



exquisite white flower clusters into grayish -white tufts, which scatter in the 
autumn gusts into hundreds of arrow-headed, spiral plumes. The achenes 







' » • • " *• 








-iff^a^ 




i 


4/) 

1 






\- 


A 


A nM nuB Ha^" , 










fC-#'f| 


• 














- ■ 




■*.»*. 


^. 


w 


U 


\ ^2^\\/ 


*** 



Fig. 485- 
Seed distribution of virgin's bower (clematis). 

have plumose styles, and the spiral form of the plume gives a curious twist 
to the falling seed (fig. 485). 



CHAPTER XLVI. 

VEGETATION IN RELATION TO ENVIRONMENT* 

I. Factors Influencing Vegetation Types. 

900. All plants are subject to the influence of environment 
from the time the seed begins to germinate until the seed is 
formed again, or until the plant ceases to live. A suitable amount 
of warmth and moisture is necessary that the seed may germi 
nate. Moisture may be present, but if it is too cold, germination 
will not take place. So in all the processes of life there are 
several conditions of the environment, or the "outside" of plants, 
which must be favorable for successful growth and reproduction. 
Not only is this true, but the surroundings of plants to a large 
extent determine the kind of plants which can grow in particular 
localities. It is also evident that the reaction of environment 
on plants has in a large measure caused them to take on certain 
forms and structures which fit them better to exist under local 
conditions. In other cases where plants have varied by muta- 
tion (p. 338) some of the new forms may be more suited to the 
conditions of environment than others and they are more apt 
to survive. These conditions of environment acting on the 
plant are factors which have an important determining influence * 
on the existence, habitat, habit, and form of the plant. These 
factors are sometimes spoken of as ecological factors, and the 
study of plants in this relation is sometimes spoken of as ecology,^ 



* For a fuller discussion of this subject by the author see Chapters XL VI- 
LV1I of his "College Text-book of Botany" (Henry Holt & Co.). 
f oiko <3= house, and Xoyo S = discourse. 

464 



FACTORS INFLUENCING VEGETATION TYPES. 465 

which means a study of plants in their home or a study of the 
household relations of plants. These factors are of three sorts: 
1st, physical factors; 2d, climatic factors; 3d, biotic factors. 

901. Physical factors. — Some of these factors are water, light, 
heat, wind, chemical or physical condition of the soil, etc. Water 
is a very important factor for all plants. Even those growing on 
land contain a large percentage of water, which we have seen is 
rapidly lost by transpiration, and unless water is available for 
root absorption the plant soon suffers, and aquatic plants are 
injured very quickly by drying when taken from the water. 
Excess of soil water is injurious to some plants. Light is impor- 
tant in photosynthesis, in determining direction of growth as 
well as in determining the formation of suitable leaves in most 
plants, and has an influence in the structure of the leaf according 
as the light may be strong, weak, etc. Heat has great influence 
on plant growth and on the distribution of plants. The growth 
period for most vegetation begins at 6° C. ( = 43° F.), or in the 
tropics at io°-i2°C, but a much higher temperature is usually 
necessary for reproduction. Some arctic algae, however, fruit 
at i.8° C. The upper limit favorable for plants in general is 
45°-5o° C, while the optimum temperature is below this. Very 
high temperatures are injurious, and fatal to most plants, but 
some algae grow in hot springs where the temperature reaches 
8o°-qo° C. Some desert plants are able to endure a temperature 
of 70 C, while some flowering plants of other regions are killed 
at 45 C. Some plants are specifically susceptible to cold, but 
most plants which are injured by freezing suffer because the 
freezing is a drying process of the protoplasm (see p. 374). Wind 
may serve useful purposes in pollination and in aeration, but 
severe winds injure plants by causing too rapid transpiration, 
by felling trees, by breaking plant parts, by deforming trees and 
shrubs, and by mechanical injuries from " sand-blast." Ground 
covers protect plants in several ways. Snow during the winter 
checks radiation of heat from the ground so that it does not 
freeze to so great a depth, and this is very important for many 
trees and shrubs. It also prevents alternate freezing and thaw- 



466 RELATION TO ENVIRONMENT. 

ing of the ground, which "heaves" some plants from the soil. 
Leaves and other plant remains mulch the soil and check evapora- 
tion of water. The influence of the chemical condition of the 
soil is very marked in alkaline areas where the concentration 
of salt in the soil permits a very limited range of species. So 
the physical and mechanical conditions of the soil influence 
plants because the moisture content of the ground is so closely 
dependent on its physical condition. Rocky and gravelly soil, 
other things being equal, is dry. Clay is more retentive of 
moisture than sand, and moisture also varies according to the 
per cent of humus mixed with it, the humus increasing the per- 
centage of moisture retained. 

902. Climatic factors. — These factors are operative over very 
wide areas. There are two climatic factors: rainfall or atmos- 
pheric moisture, and temperature. A very low annual rainfall 
in warm or tropical countries causes a desert; an abundance of 
rain permits the growth of forests; extreme cold prevents the 
growth of forests and gives us the low vegetation of arctic and 
alpine regions. 

903. Biotic factors. — These are animals which act favorably 
in pollination, seed distribution, or unfavorably in destroying or 
injuring plants, and man himself is one of the great agencies 
in checking the growth of some plants while favoring the growth 
of others. Plants also react on themselves in a multitude of 
ways for good or evil. Some are parasites on others; some in 
symbiosis (see p. 85) aid in providing food; shade plants are 
protected by those which overtop them; mushrooms and other 
fungi disintegrate dead plants to make humus and finally plant 
food; certain bacteria by nitrification prepare nitrates for the 
higher plants (see p. 83). 

II. Vegetation Types and Structures. 

904. Responsive type of vegetation. — In studying vegetation 
in relation to environment we are more concerned with the 
form of the plants which fits them to exist under the local con- 



VEGETATION TYPES AND STRUCTURES. 467 

ditions than we are with the classification of plants according 
to natural relationships. Plants may have the same vegetation 
type, grow side by side, and still belong to very different floristic 
types. For example, the cactus, yucca, three-leaved sumac, 
the sage-brush, etc., have all the same general vegetation type 
and thrive in desert regions. The red oaks, the elms, many 
goldenrods, tri Ilium, etc., have the same general vegetation type, 
but represent very different floristic types. The latter plants 
grow in regions with abundant rainfall throughout the year, 
where the growing -season is not very short and temperature 
conditions are moderate. Some goldenrods grow in very sandy 
soil which dries out quickly. These have fleshy or succulent 
leaves for storing water, and while they are of the same floristic 
type as goldenrods growing in other places, the vegetation type 
is very different. The types of vegetation which fit plants for 
growing in special regions or under special conditions, they have 
taken on in response to the influence of the conditions of their envi- 
ronment. While we find all gradations between the different types 
of vegetation, looking at the vegetation in a broad way, several 
types are recognized which were proposed by Warming as follows: 

905. Mesophytes. — These are represented by land plants 
under temperate or moderate climatic and soil conditions. The 
normal land vegetation of our temperate region is composed 
of mesophytes, that is ; the plants have mesophytic structures 
during the growing season. The deciduous forests or thickets 
of trees and shrubs with their undergrowth, the meadows, pas- 
tures, prairies, weeds, etc., are examples. In those portions 
of the tropics where rainfall is great the vegetation is mesophytic 
the year around. 

906. Xerophytes. — These are plants which are provided with 
structures which enable them to live under severe conditions 
of dryness, where the air and soil are very dry, as in deserts or 
semideserts, or where the soil is very dry or not retentive of 
moisture, as in very sandy soil which is above ground water, or 
in rocky areas. Since the plants cannot obtain much water 
from the soil they must be provided with structures which will 



468 RELATION TO ENVIRONMENT. 

enable them to retain the small amount they can absorb from 
the soil and give it off slowly. Otherwise they would dry out 
by evaporation and die. Some of the structures which enable 
xerophytic plants to withstand the conditions of dry climate 
and soil are lessened leaf surface, increase in thickness of leaf, 
increase in thickness of cuticle, deeply sunken stomates, compact 
growth, also succulent leaves and stems, and in some cases loss 
of the leaf. Evergreens of the north temperate and the arctic 
regions are xerophytes. 

907. Hydrophytes,— These are plants which grow in fresh 
water or in very damp situations. The leaves of aerial 
hydrophytes are very thin, have a thin cuticle, and lose water 
easily, so that if the air becomes quite dry they are in danger of 
drying up even though the roots may be supplied with an abun- 
dance of water. The aquatic plants which are entirely submerged 
have often thin leaves, or very finely divided or slender leaves, 
since these are less liable to be torn by currents of water. The 
stems are slender and especially lack strengthening tissue, since 
the water buoys them up. Removed from the water they droop 
of their own weight, and soon dry up. The stems and leaves 
have large intercellular spaces filled with air which aids in aera- 
tion and in the diffusion of gases. Some use the term hygrophytes. 

908. Halophytes. — These are salt-loving plants. They grow 
in salt water, or in salt marshes where the water is brackish, 
or in soil which contains a high per cent of certain salts, for example 
the alkaline soils of the West, especially in the so-called "Bad 
Lands" of Dakota and Nebraska, and in alkaline soils of the 
Southwest and California. These plants are able to withstand 
a stronger concentration of salts in the water than other plants. 
They are also found in soil about salt springs. 

909. Tropophytes.* — Tropophytes are plants which can live as 
mesophytes during the growing season, and then turn to a 
xerophytic habit in the resting season. Deciduous trees and 
shrubs, and perennial herbs of our temperate regions, are in 
this sense tropophytes, while many are at the same time mesophytes 

* Term used by Schimper. 



PLANT FORMATIONS. 469 

if they exist in the portions of the temperate region where rain- 
fall is abundant. In the spring and summer they have broad 
and comparatively thin leaves, transpiration goes on rapidly, 
but there is an abundance of moisture in the soil, so that root 
absorption quickly replaces the loss and the plant does not 
suffer. In the autumn the trees shed their leaves, and in this 
condition with the bare twigs they are able to stand the drying 
effect of the cold and winds of the winter because transpiration 
is now at a minimum, while root absorption is also at a minimum 
because of the cold condition of the soil. Perennial herbs like 
trillium, dentaria, the goldenrods, etc., turn to xerophytic habit 
by the death of their aerial shoots, while the thick underground 
shoot which is also protected by its subterranean habit carries 
the plant through the winter. 

910. While these different vegetation types are generally 
dominant in certain climatic regions or under certain soil con- 
ditions, they are not the exclusive vegetation types of the regions. 
For example, in desert or semidesert regions the dominant 
vegetation type is made up of xerophytes. But there is a 
mesophytic flora even in deserts, which appears during the 
rainy season where temperature conditions are favorable for 
growth. This is sometimes spoken of as the rainy-season flora. 
The plants are annuals and by formation of seed can tide over 
the dry season. So in the region where mesophytes grow there 
are xerophytes, examples being the evergreens like the pines, 
spruces, rhododendrons; or succulent plants like the stonecrop, 
the purslane, etc. Then among hydrophytes the semiaquatics 
are really xerophytes. The roots are in water, and absorption 
is slow because there are no root hairs, or but few, and the aerial 
parts of the plant are xerophytic. 

III. Plant Formations. 

911. The term plant formation is applied to associations of 
plants of the same kind, though there is a great difference in the 
use of the word by different writers which leads to some con- 



47° RELATION TO ENVIRONMENT. 

fusion.* It is sometimes applied to an association of individuals 
of a species, or of several species occupying a rather definite area 
of ground where the soil conditions are not greatly different 
(individual formation); by others it is applied to the plants of 
a definite physiographic area, as a swamp, moor, strand, or 
beach, bank, rock hill, clay hill, ravine, bluff, etc. (principal for- 
mation) ; and in a broad sense it is applied to the plants of climatic 
regions, of those in bodies of water, etc. (general formations). 
Space here is too limited to discuss all these kinds of formations, 
but the nature of the general formations will be pointed out. 
The general formations may be grouped into four divisions: 

ist. Climatic formations. 

2d. Edaphic formations. 

3d. Aquatic formations. 

4th. Culture formations. 
912. Climatic formations. — Climatic influences extend over 
wide regions, so that climate controls the general type of vegeta- 
tion of a region. In the sense of control there are two climatic 
factors, temperature and moisture, especially soil moisture. 
Temperature exerts a controlling influence over the vegetation 
type only where the total heat during the period of growth and 
reproduction is very low. This occurs in polar lands and at 
high elevations where the climate is alpine. In the temperate 
and tropical regions of the globe moisture, not heat, controls 
the general vegetation type. These vegetation types in general 
are coincident with rainfall distribution, and Schimper recognizes 
here three types, which with the arctic-alpine type would make 
four climatic formations as follows: 

1 st. The woodland, formation. — This formation is characterized 
by trees and shrubs, and it is what is called a close formation. 
By this it is meant that so far as the climate is concerned the 
conditions are favorable for the development of trees and shrubs 
in such abundance that they become the dominant vegetation 
type of the region and grow close together. Other plants, as 



* See the author's " College Text-book of Botany." Chapter XLIX. 



PLANT FORMATIONS. 47 1 

herbs, grasses, etc., occur, but they grow as subordinate elements 
of the general vegetation type, and as undergrowth. The 
land portion of the globe, therefore, outside of arctic and alpine 
regions, where the annual precipitation is 40 to 60 or more inches, 
is the area for woodland formation. In some places, the 
eastern part of England, for example, the annual precipitation 
is 25 to 30 inches, but the cool temperature permits a forest 
growth. It is true there are places where forests do not grow, — 
where man cuts them down, for example. But if cultivated lands 
in this region were allowed to go to waste, they would in time grow 
up to forest again. So there are swamps where the soil is too 
wet for trees, or sandy or rocky areas where there is not a suf- 
ficient amount of soil or water to support forest trees. But 
here it is the soil conditions, not climatic conditions, which pre- 
vent the development of the forest. But we know that swamps 
are being filled in and the ground gradually becoming higher 
and drier, and that soil is slowly accumulating in rocky areas, 
so that in time if left to natural forces these places would become 
forested. So this area of heavy annual rainfall is a -potential 
forest area. These areas are determined by warm currents of 
moisture-laden air from the ocean moving over cooler land areas 
where the moisture is precipitated. In general these areas are 
along the coasts of great continents and on mountains. There- 
fore the interior of a continent is apt to be dry because most 
of the moisture has been precipitated before it reaches the interior. 
Deserts or steppes are therefore usually near the interior of 
continents. Some exceptions to this general rule are found: 
central South America, which is a region of exceptional rainfall 
because the moisture-laden winds here come from the warmest 
part of the ocean; the desert region west of the Andes mountains, 
where the winds are not favorable; southern California, where 
the winds come chiefly from a cooler portion of the Pacific ocean 
and move over an area of high temperature, etc. 

2d. Grassland formation. — Grasses form the dominant vege- 
tation type where the annual rainfall is approximately 15 to 25 
inches. In true grasslands the formation is a close one since 



472 



RELATION TO ENVIRONMENT. 



there is still a sufficient amount of moisture to provide for all 
the plants which can stand on the ground. Yet there is not 
enough moisture to permit the growth of forest as the dominant 
type without aid and protection by man. The so-called prairie 
regions are examples. Trees and shrubs do occur, but they 
cannot compete successfully with the grasses because the climatic 




Fig. 486. 
Typical prairie scene, a few miles west of Lincoln, Nebraska. (Bot. Dept., Univ. 
Nebraska. ) 

conditions are favorable for the latter and unfavorable for the 
former. On the border line between forest and prairie the line 
of division is not a clear-cut one because conditions grade from 
one to the other. The two formations are somewhat mixed, 
like the outposts of contending armies, arms of the forest or 
prairie extending out here and there. In the United States the 
prairies extend from Illinois to about the 100th meridian, and 
beyond this to the foothills of the Rockies and southwest to the 
Sonora Nevada desert the region is drier, the rainfall varying 
from 10 to 20 inches. This is the area of the Great Plains, 
and while grasses of the bunch type are dominant, they make 



PLANT FORMATIONS. 473 

a more or less open formation because the moisture is not suf- 
ficient to supply all the plants which could be crowded on the 
ground, each individual tuft needing an area of ground surround- 
ing it on which it can draw for moisture. Such a formation is 
an open one, and in this respect is similar to desert formations. 
3d. Desert formations. — These occur where the annual rain- 
fall is still lower, 10 to 4 inches or even less, 2 to 3 inches, while 
in one place in Chili it is as low as J inch. In the great Sahara 
desert it is about 8 inches, while in the Sonora Nevada desert 











HE 










(tfWJW''.** 









Fig. 487. 
Winter range in northwestern Nevada, showing open formation; white sage 
(Eurotia lanata) in foreground, salt-bush (Atriplex confertifolia) and bud-sage 
(Artemisia spinescens) at base of hill, red sage (Kochia americana) on the higher 
slope. (After Griffiths, Bull. 38, Bureau Plant Ind., U. S. Dept. Agr.) 

in the southwestern United States it is 4 to 8 inches. Here 
the formation is an open one. In the forest and prairie forma- 
tions the plants compete with each other for occupancy of the 
ground, since climatic conditions are favorable, so that the struggle 
against climate is not severe. But in the desert plants do not com- 
pete with each other; since the climate is so austere, the struggle 
is against the climate. Hence plants stand at some distance from 
each other because the roots need the moisture from the ground 
for some distance around them. There is not enough moisture 
for all the plants that begin, and those which get the start take 



474 



RELATION TO ENVIRONMENT. 



the moisture away from the intervening ones, which then die. 
Since the struggle is against the adverse conditions of climate 
and not a competition between plants to occupy the ground, 
no one rloristic type dominates as in the case of the grasses and 
forests of the grassland and woodland formations, but grass- 
land and woodland types grow together. So we find grasses, 
trees, and shrubs growing without competition in the desert. 
The dominant vegetation type is xerophytic. 

4th. Arctic-alpine formation. This formation extends from 
the limit of tree growth to the region of perpetual ice and snow. 




Fig. 488. 
Northern limit of tree growth, Alaska. (Copyright, 1899, by E. H. Harriman.) 

The forest here comes in competition with climate, with the 
severe cold of the long winter night, so that tree growth is limited, 
and on the border line with the woodland formation the trees 
are stunted, bent to one side by the heavy snows, or the tops are 
killed by the cold wind. The arctic zone of plant growth is 
sometimes spoken of as the "cold waste," since conditions here 
are somewhat similar to those in the desert, the extreme cold 



PLANT SOCIETIES. 47$ 

exercising a drying effect on vegetation, and the vegetation type 
then is largely xerophytic. 

913. Edaphic * formations. — Edaphic formations may occur 
in any of the climatic-formation areas. They are controlled by 
the condition of soil or ground. The condition of the soil is 
unfavorable for the growth of the general vegetation type of 
that region, or is more favorable for another vegetation type, so 
that soil conditions overcome the climatic conditions. These 
areas include swamps, moors, the strand or beach, rocky areas, 
etc., as well as oases in the desert, warm oases in the arctic zone, 
river bottoms in the prairie and plains region, alkaline areas, etc. 
The edaphic formations may be close or open according to the 
nature of the soil. The edaphic formations then are infiltrated 
in the climatic formations, the different vegetation types fitting 
together like pieces of mosaic, which can be seen in some places 
from a mountain top, or if one could take a bird's-eye view of 
the landscape or from a balloon. 

914. Aquatic formations. — These are made up of water 
plants and are of two general kinds: fresh- water plant forma- 
tions in ponds, lakes, streams; and salt-water plant formations 
in the ocean and inland salt seas. 

915. Culture formations. — Culture formations are largely 
controlled by man, who destroys the climatic or edaphic forma- 
tion and by cultivation protects cultivated types, or by allowing 
land to go to "waste" permits the growth of weeds, though 
weeds are often abundant in the culture areas. In general the 
culture formations may be grouped into two subdivisions: ist, the 
vegetation of cultivated places; and 2d, the vegetation of waste 
places, as abandoned fields, roadsides, etc. 

IV. Plant Societies. 

916. Plant societies are somewhat definite associations of 
the vegetation of an area marked by physiographic conditions. 
A single plant society is nearly if not altogether identical with a 

* e5a<po < 3 = ground. 



476 RELATION TO ENVIRONMENT. 



1 1 



principal formation" but is a more popular expression, and 
besides includes all the plants growing on the area, while in the 
use of the term "principal formation" we have reference mainly 
to the dominant plants and the most conspicuous subordinate 
species. 

917. Complex character of plant societies. — In their broadest 
analysis all plant societies are complex. Every plant society 
has one or several dominant species, the individuals of which, 
because of their number and size, give it its peculiar character. 
The society may be so nearly pure that it appears to consist of 
the individuals of a single species. But even in those cases 
there are small and conspicuous plants of other species which 
occupy spaces between the dominant ones. Usually there are 
several or more kinds in the same society. The larger individuals 
come into competition for first place in regard to ground and 
light, the smaller ones come into competition for the intervening 
spaces for shade, and so on down in the scale of size and shade 
tolerance. Then climbing plants (lianas) and epiphytes (lichens, 
algae, mosses, ferns, tree orchids, etc.) gain access to light and sup- 
port by growing on other larger and stouter members of the society. 
Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, 
etc.) are present, either actually or potentially, in all societies, 
and in their methods of obtaining food sap the life and health 
of their hosts. Then come the scavenger members, whose 
work it is to clean house, as it were, the great army of saprophytic 
fungi (molds, mushrooms, etc.), and bacteria ready to lay hold 
on dead and dying leaves, branches, trunks, roots, etc., disin- 
tegrate them, and reduce them to humus, where other fungi 
change them into a form in which the larger members of the 
plant society can utilize them as plant food and thus continue 
the cycle of matter through life, death, decay, and into life again. 
Mycorhiza (see Chapter IX) or other forms of mutualistic 
symbiosis occur which make atmospheric nitrogen available for 
food, or shorten the path from humus to available food, or the 
humus plants feed on the humus directly. Nor should we 
leave out of account the myriads of nitrate and nitrite bacteria 



PLANT SOCIETIES. 477 

(see Chapter IX) which make certain substances in the soil avail- 
able to the higher members of the society. Most plant societies 
are also benefited or profoundly influenced in other ways by 
animals, as the flower-visiting insects, birds which feed on 
injurious insects, the worms which mellow up the soil and cover 
dead organic matter so that it may more thoroughly decay. In 
short, every plant society is a great cosmos like the universe 
itself of which it is a part, where multitudinous forms, processes, 
influences, evolutions, degenerations, and regenerations are at 
work. 

918. Forest Societies.* — Each different climatic belt or region 
has its characteristic forest. For example, the forests of the 
Hudsonian zone in North America are different from those of 
the Canadian zone, and these in turn different from those in 
the transition zone (mainly in northern United States). The 
forests of the Rocky mountains and of the Pacific coast differ 
from those of the Alleghanian, Carolinian (mainly middle United 
States) or Austroriparian (southern United States) areas. 
Finally, tropical forests are strikingly different from those of 
other regions. Similar variations occur in the forests of other 
regions of the globe. The character of these forests depends 
largely on climatic factors. The character of the forest varies, 
however, even in the same climatic area, dependent on soil 
conditions, or success in seeding and ground-gaining of the 
different species in competition, etc. 

919. General structure of the forest. — Structurally the forest 
possesses three subdivisions: the floor, the canopy, and the 
interior. The floor is the surface soil, which holds the rootage 
of the trees, with its covering of leaf-mold and carpet of leaves, 
mosses, or other low, more or less compact vegetation. The 
canopy is formed by the spreading foliage of the tree crowns, 
which, in a forest of an even and regular stand, meet and form 
a continuous mass of foliage through which some light filters 
down into the interior. Where the stand is irregular, i.e., the 

* For a full discussion of forest societies see Chapter L in the author's 
"College Text-book of Botany." 



473 



RELATION- TO ENVIRONMENT. 



trees of different heights, the canopy is said to be " compound" 
or "storied." Where it is uneven, there are open places in 
the canopy which admit more light, in which case the under- 
growth may be different. The interior of the forest lies between 
the canopy and the floor. It provides for aeration of the floor 
and interior occupants, and also room for the boles or tree trunks 




Fig. 489. 
Mature forest of redwood (Sequoia sempervirens). 
Dept. Agr., Bull. 38.) 



(Bureau of Forestry, U. S. 



(called by foresters the wood mass of the forest) which support 
the canopy and provide the channels for communication and 
food exchange between the floor and canopy. The canopy 
manufactures the carbohydrate food and assimilates the mineral 
and proteid substances absorbed by the roots in the soil; and 
also gets rid of the surplus water needed for conveying food 
materials from the floor to the place where they are elaborated. 
It is the seat where energy is created for work, and also the 
place for seed production. 



PLANT SOCIETIES. 479 

920. Longevity of the forest. — The forest is capable of self- 
perpetuation, and, except in case of unusual disaster or the action 
of man, it should live indefinitely. As the old trees die they 
are gradually replaced by younger ones. So while trees may 
come and trees may go, the forest goes on forever. 

921. Autumn colors. — One of the striking effects produced 
by the deciduous forests is that of the autumn coloring of the 
leaves. It is more pronounced in the forests of the United States 
than in corresponding life zones in the eastern hemisphere because 
of the greater number of species. With the disintegration of 
the chlorophyll bodies, other colors, which in some cases were 
masked by the green, appear. In other cases decomposition 
products result in the formation of other colors, as red, scarlet, 
yellow, brown, purple, maroon, etc., in different species. These 
coloring substances to some extent are believed to protect the 
nitrogenous substances in the leaf from injury. The colors 
absorb the sun's rays, which otherwise might destroy these 
nitrogenous substances before they have passed back through 
the petiole of the leaf into the stem, where they may be stored 
for food. The gorgeous display of color, then, which the leaves 
of many trees and shrubs put on is one of the many useful adapta- 
tions of the plants. 

922. Importance of the forest in the disposal of rainfall. — The 
importance of the forest in disposing of the rainfall is very great. 
The great accumulation of humus on the forest floor holds back 
the water both by absorption and by checking its flow, so that 
it does not immediately flow quickly off the slopes into the drain- 
age system of the valley. It percolates into the soil. Much 
of it is held in the humus and soil. What is not retained thus 
filters slowly through the soil and is doled out more gradually 
into the valley streams and mountain ttributaries, so that the 
flood period is extended, and its injury lessened or entirely pre- 
vented, because the body of water moving at any one time is 
not dangerously high. The winter snow is shaded and in the 
spring melts slowly, and the spring freshets are thus lessened. 
The action of the leaves and humus in retarding the flow of the 



480 RELATION TO ENVIRONMENT. 

water prevents the washing away of the soil; the roots of trees 
bind the soil also and assist in holding it. 

923. Absence of forest encourages serious floods. — The great 
floods of the Mississippi and its tributaries are due to the rapidity 
with which heavy rainfall flows from the rolling prairies of the 
west, and from the deforested areas west of the Alleghany system. 
The serious floods in recent years in some of the South Atlantic 
States are in part due to the increasing area of deforestation in 
the Blue Ridge and southern Alleghany system. 

924. The prairie and plains societies. — These are to be found 
in the grassland formation. In the prairies "meadows" are 
formed in the lower ground near river courses where there is 
greater moisture in soil. The grasses here are principally " sod- 
formers" which have creeping underground stems which mat 
together, forming a dense sod. On the higher and drier ground 
the "bunch" grasses, like buffalo-grass, beard-grass, or broom- 
sedge, etc., are dominant, and in the drier regions as one 
approaches desert conditions the vegetation gradually takes on 
more the character of the desert, so that in the plains sage- 
brush, the prickly-pear cactus, etc., occur. Besides the dominant 
vegetation of the society there are subordinate species, and the 
societies are especially marked by a spring and autumn flora of 
conspicuous flowering plants which are mixed with the grasses. 

925. Desert societies. — These are composed of plants which 
possess a form or structure which enables them to exist in a 
very dry climate where the air is very dry and the soil contains 
but little moisture. The true desert plants are perennial. The 
growth and flowering period occurs during the rainy season, or 
those portions of the rainy season when the temperature is favor- 
able, and they rest during the very dry season and cold. Charac- 
teristic desert plants are the cacti with thick succulent green 
stems or massive trunks, the leaves being absent or reduced to 
mere spines which no longer function in photosynthesis; yuccas 
with thick, narrow and long leaves with a firm and thick cuticle; 
small shrubs or herbs with compact rounded habit and small 
thick gray leaves. All of these structures conserve moisture. 



PLANT SOCIETIES. 



481 



The mesquite tree is one of the common trees in portions of the 
Sonora Nevada desert. Besides the true desert plants, desert 
societies have a rainy-season flora consisting of annuals, which 




Fig. 490. 
Desert vegetation, Arizona, showing large succulent trunks of cactus with shrubs 
and stunted trees. Open formation. (Photograph by Tuomey.) 



can germinate, vegetate, flower, and seed during the period of 
rain and before the ground moisture has largely disappeared, 
and these pass the resting period in seed. 

926. Arctic-alpine societies. — The most striking of the arctic 
plant societies are the "polar tundra," extensive mats of vegeta- 
tion largely made up of mosses, lichens, etc., only partially 
decayed because of the great cold of the subsoil, and perhaps 
also because of humus acid in the partially decayed vegetation. 
These tundras are brightened by numerous flowering plants 
which are characterized by short stems, a rosette of leaves near 
the ground, and by large bright-colored flowers. Heaths, saxi- 
frages, and dwarf willow abound. Alpine-plant societies are 
similar to the arctic, although some of the conditions are more 



482 RELATION TO ENVIRONMENT. 

severe than in the arctic region. This is principally due to the 




Fig. 491. 
Polar tundra with scattered flowers, Alaska. (Copyright by E. H. Harriman.) 

fact that during the summer while the plants are growing they 



Vs &~TA 



msBSg^* 




Fig. 492. 
Perennial rosette plant from alpine flora of the Andes, showing short stem, 
rosette of leaves, and large flower. (After Schimper.) 

are subject to a high temperature during the day and a very low 



PLANT SOCIETIES. 483 

temperature at night, whereas during the summer in arctic regions 
while the plants are growing there is continuous warmth for growth 
and continuous light for photosynthesis. Five types of alpine 
plants are recognized by some. 1st. Elfin tree. This type has 
short, gnarled, often horizontal stems, as seen in pines, birches, 
and other trees growing in alpine heights. 2d. The alpine shrubs. 
In the highest alpine belts they are dwarfed and creeping, richly 
branched and spreading close to the ground, while at lower belts 
they are more like lowland shrubs. 3d. The cushion type. 
The branching is very profuse and the branches are short and 
touch each other on all sides, forming compact masses (examples 
saxifrages, androsace, mosses, etc.). 4th. Rosette plants. These 
are perennial, short stems and very strong roots, and play an 
important part in the alpine meadows. 5th. Alpine grasses. 
These usually have much shorter leaves than grasses of the low- 
lands and consequently form a low sward. 

927. Edaphic plant societies. — These are equivalent to edaphic 
plant formations, and the vegetation is of course controlled by 
the peculiar conditions of the soil. There are a number of 
different kinds of edaphic plant societies determined by the 
character of the physiographic areas. 1st. Sphagnum moors. 
These are formed in shallow basins originally with more or less 
water. The growth of the sphagnum moss along with other 
vegetation and its partial decay in the water builds up ground 
rapidly so that in course of time the pond may be completely 
filled in. This filling in proceeds from the shore toward the 
center, and in the early stages of course there would be a pond 
in the center. The partial decay of vegetation creates an excess 
of humus acid which retards absorption by the roots. The 
conditions are such, then, as require aerial structures for retarding 
the loss of water, and plants growing in such moors are usually 
xerophytes. Some of the plants are identical with those growing 
in the arctic tundra. 2d. Sand * strand of beach. The quantity 
of sand with very little or no admixture of humus or plant food 
makes it difficult for plants to obtain a sufficient amount of 

* See Chapter LIV of the author's "College Text-book of Botany." 



4$4 



RELATION TO ENVIRONMENT. 



water even where rainfall is abundant. The same may be said 
of the sand dunes farther back from the shore. The plants 
of these areas are then usually xerophytes. Some of the plants 
accustomed to growing in such localities are American sea-rocket, 
seaside spurge, bugseed, sea-blite, sea-purslane, the sand- 
cherry, dwarf willow, marram-grass, certain species of beard- 
grass, etc. 3d. Rocky shores or areas. Here lichens and mosses 
first grow, later to be followed by herbs, grasses, shrubs, and 
trees, as decayed plant remains accumulate in the rock crevices. 
4th. Shores of ponds, or swamp moors. Here the vegetation 
often takes on a zonal arrangement if the ground gradually 
slopes to the shore and out into the pond. In Fig. 493 is shown 




Fig. 493- 
Macrophytes in the upper zone of the photic region. Ascophyllum and Fucus 
at low tide, Hunter's Island, New York City. (Photograph by M. A. Howe.) 



zonal distribution of plants. The different kinds of plants are 
drawn into these zones by the varying amount of ground water 
in the soil, or the varying depth of the water on the margin of 
the pond as one proceeds from the land towards the deeper 
water. On the border lines or tension lines between the different 
zones the plants are struggling to occupy here ground which is 
suitable for each adjacent individual formation. Other edaphic 
societies are those of marl ponds, alkaline areas, oases in deserts, 



PLANT SOCIETIES. 



485 




M 

<& 
i-l 

03 

P 
>> 

<& 
O 

o 

CO 

. 3 
tJ- O 
O CO 






486 RELATION TO ENVIRONMENT 

warm oases in arctic lands, the forested areas along river bottoms 
in prairie or plains regions, etc. 

928. Aquatic plant societies — In general we might distinguish 
three kinds, ist. Fresh-water -plant societies , with floating algae 
like spirogyra, cedogonium, etc., the floating duck-meats, riccias; 
the plants of the lily type with roots and stems attached to the 
bottom and leaves floating on the surface, like the water-lily 
and certain pondweeds, and finally the completely submerged 
ones like certain pondweeds, the bassweed (Chara), etc. 
2d. Marine plant societies, which are made up mostly of the 
red and brown algae or "seaweeds," though some green algae 
and flowering plants also occur. 3d. The salt marshes where 
the water is brackish and there is usually a luxuriant growth of 
marsh-grasses. 



CHAPTER XLVII. 

CLASSIFICATION OF THE ANGIOSPERMS. 

Relation of Species, Genus, Family, Order, etc. 

929. Species. — It is not necessary for one to be a botanist in 
order to recognize, during a stroll in the woods where the tril- 
lium is flowering, that there are many individual plants very 
like each other. They may vary in size, and the parts may 
differ a little in form. When the flowers first open they are 
usually white, and in age they generally become pinkish. In 
some individuals they are pinkish when they first open. Even 
with these variations, which are trifling in comparison with the 
points of close agreement, we recognize the individuals to be of 
the same kind, just as we recognize the corn plants, grown from 
the seed of an ear of corn, as of the same kind. Individuals of 
the same kind, in this sense, form a species. The white wake- 
robin, then, is a species. 

But there are other trilliums which differ greatly from this one. 
The purple trillium (T. erectum) shown in fig. 495 is very different 
from it. So are a number of others. But the purple trillium 
is a species. It is made up of individuals variable, yet very like 
one another, more so than any one of them is like the white 
wake-robin. 

930. Genus. — Yet if we study all parts of the plant, the 
perennial root-stock, the annual shoot, and the parts of the 
flower, we find a great resemblance. In this respect we find 
that there are several species which possess the same general 
characters. In other words, there is a relationship between 

487 



488 



CLASSIFICATION OF ANGIOSPERMS. 



these different species, a relationship which includes more than the 

individuals of one kind. It includes several kinds. Obviously, 

then, this is a relationship 

with broader limits, and 

of a higher grade, than 

that of the individuals of 

a species. The grade next 

higher than species we 

call genus. Trillium, 

then, is a genus. Briefly 

the characters of the genus 

tri Ilium are as follows: 

931. Genus trillium. — Perianth of 
six parts: sepals 3, herbaceous, per- 
sistent; petals colored. Stamens 6 (in 
two whorls), anthers opening inward. 
Ovary 3-loculed, 3-6-angled; stig- 
mas 3, slender, spreading. 
Herbs with a stout per- 
ennial rootstock, with 
fleshy, scale-like leaves, 
from which the low annual 
shoot arises, bearing a terminal flower and 3 large netted-veined 
leaves in a whorl. 

Note. — In speaking of the genus the present usage is to say 
trillium, but two words are usually employed in speaking of the 
species, as Trillium grandiflorum, T. erectum, etc. 

932. Genus erythronium. — The yellow adder-tongue, or 
dogtooth violet (Erythronium americanum), shown in fig. 496, 
is quite different from any species of trillium. It differs more 
from any of the species of trillium than they do from each 
other. The perianth is of six parts, light yellow, often spotted 
near the base. Stamens are 6. The ovary is obovate, tapering 
at the base, 3-valved, seeds rather numerous, and the style is 
elongated. The flower stem, or scape, arises from a scaly bulb 
deep in the soil, and is sheathed by two elliptical-lanceolate, 




Fig. 49 5- 
Trillium erec- 
tum (purple 
f o rm ) , two 
plants from one 
rootstock. 



GENUS. FAMILY, ETC. 



489 



mottled leaves. The smaller plants have no flower and but 

one leaf, while the 

bulb is nearer the 

surface. Each year 

new bulbs are 

formed at the end 

of runners from a 

parent bulb. These 

runners penetrate 

each year deeper 

into the soil. The 

deeper bulbs bear 

the flower stems. 

933. Genus lil- 
ium. — While the 
lily differs from 
either the trillium 
or erythronium, yet 
we recognize a re- 
lationship when we 
compare the peri- 
anth of six col- 
ored parts, the 6 
stamens, and the 
3 -sided and long 
3-loculed ovary. 

934. Family Liliaceae. — The relationship between genera, as 
between trillium, erythronium, and lilium, brings us to a still 
higher order of relationship, where the limits are broader than in 
the genus. Genera which are thus related make up the family. 
In the case of these genera the family has been named after the 
lily, and is the lily family, or Liliacece. 

935. Order, class, group. — In like manner the lily family, 
the iris family, the amaryllis family, and others which show 
characters of close relationship are united into an order which 
has broader limits than the family. This order is the lily order, 




Fig. 406. 
Adder-tongue (erythronium). At left below pistil, and 
three stamens opposite three parts of the perianth. Bulb 
at the right. 



490 



CLASSIFICATION OF ANGIOSPERMS, 



or order Liliales. The various orders unite to make up the class, 
and the classes unite to form a group. 

936. Variations in usage of the terms class, order, etc. — 

Thus, according to the system of classification adopted by some, 
the angiosperms form a group. The group angiosperms is then 
divided into two classes, the monocotyledones and dicotyledones. 
(It should be remembered that all systematists do not agree in 
assigning the same grade and limits to the classes, subclasses, 
etc. For example, some treat of the angiosperms as a class, 
and the monocotyledons and dicotyledons as subclasses; while 
others would divide the monocotyledons and dicotyledons into 
classes, instead of treating each one as a class or as a subclass. 
Systematists differ also in usage as to the termination of the 
ordinal name; for example, some use the word Liliales for Lilii- 
florce, in writing of the order.) 

937. Monocotyledones. — In the monocotyledons there is a 
single cotyledon on the embryo; the leaves are parallel veined; 
the parts of the flower are usually in threes; endosperm is usu- 
ally present in the seed; the vascular bundles are usually closed, 
and are scattered irregularly through the stem as shown by a 




Fig. 497- 

A. Cross-section of the stem of an oak tree thirty-seven years old, showing the 
annual rings, rm, the medullary rays; m, the pith (medulla). B. Cross-section 
of the stem of a palm tree, showing the scattered bundles. 

cross-section of the stem of a palm (fig. 497), or by the arrange- 
ment of the bundles in the corn stem (fig. 57). Thus a single 
character is not sufficient to show relationship in the class (nor 



ORDER, CLASS, GROUP. 49 1 

is it in orders, nor in many of the lower grades), but one must 
use the sum of several important characters. 

938. Dicotyledones. — In the dicotyledons there are two 
cotyledons on the embryo; the venation of the leaves is reticu- 
late; the endosperm is usually absent in the seed; the parts of the 
flower are frequently in fives; the vascular bundles of the stem 
are generally open and arranged in rings around the stem, as shown 
in the cross-section of the oak (fig. 497). There are exceptions 
to all the above characters, and the sum of the characters must 
be considered, just as in the case of the monocotyledons. 

939. Taxonomy. — This grouping of plants into species, 
genera, families, etc., according to characters and relationships 
is classification, or taxonomy. 

To take Trillium grandiflorum for example, its position in 
the system, if all the principal subdivisions should be included 
in the outline, would be indicated as follows: 
Group, Angiosperms. 
Class, Monocotyledones. 
Order, Liliales. 
Family, Liliaceae. 
Genus, Trillium. 

Species, grandiflorum. 
In the same way the position of the toothwort would be indi- 
cated as follows: 

Group, Angiosperms. 
Class, Dicotyledones. 
Order, Papaverales. 
Family, Cruciferae. 
Genus, Dentaria. 
Species, diphylla. 
But in giving the technical name of the plant only two of 
these names are used, the genus and species, so that for the 
toothwort we say Dentaria diphylla, and for the white wake- 
robin we say Trillium grandiflorum. 

940. Kingdom and Subkingdom. — Organic beings form alto- 
gether two kingdoms, the Animal Kingdom and the Plant King- 



49 2 CLASSIFICATION. 

dom. The Plant Kingdom is then divided into a number of 
subkingdoms as follows: ist, Subkingdom Thallophyta, the 
thallus plants, including the Algae and Fungi; 2d, Subkingdom 
Bryophyta, the moss-like plants, including the Liverworts and 
Mosses; 3d, Subkingdom Pteridophyta, the fern-like plants, 
including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th, Sub- 
kingdom Spermatophyta, the seed-plants, including Gymno- 
sperms and Angiosperms. Subkingdoms are divided into groups 
of lower order down to the classes. So there are subclasses, 
subfamilies or tribes, subgenera, and even subspecies. But 
taking the principal taxonomic divisions from the greater to the 
lesser rank, the order would be as follows: 

Plant Kingdom. 

Subkingdom, Spermatophyta. 

Group (not used in a definite sense). 
Class, Gymnospermae. 
Order, Pinales. 
Family, Pinaceae. 
Genus, Pinus. 

Species, strobus, or, in full, 
Pinus strobus, the white pine. 

Group Angiospermae. 

I. CLASS MONOCOTYLEDONES. 

941. Order Pandanales. — Aquatic or marsh plants. The 
cattail flags (Typha) and the bur-reeds (Sparganium), each rep- 
resenting a family. The name of the order is taken from 
the tropical genus Pandanus (the screw-pine often grown in 
green-houses). 

942. Order Naiadales. — Aquatic or marsh herbs. Three 
families are mentioned here. 

The pondweed family (Naiadaceae), named after one genus, 
Naias. The largest genus is Potamogeton, the species of which 
are known as pondweeds. Ruppia occidentalis occurs in 



ORDERS OFANGIOSPERMS. 493 

saline ponds in Nebraska, and R. maritima along the seacoast 
and in saline districts in the interior. 

The water-plantain family (Alismaceae) includes the water- 
plantain (Alisma) and the arrow-leaves (Sagittaria). 

The tape-grass family (Vallisneriaceae) includes the tape-grass, 
or eel-grass (the curious Vallisneria spiralis). 

943. Order Graminales. — Two families. 

The grass family (Gramineae), the grasses and grains. 
The sedge family (Cyperaceae) , the sedges. 

944. Order Palmales, with one family, Palmaceae, includes 
the palms, abundant in the tropics and extending into Florida. 
Cultivated in greenhouses. 

945. Order Arales. 

The arum family (Araceae). Flowers in a fleshy spadix. Ex- 
amples: Indian turnip (Arisaema), sweet-flag (Acorus), skunk- 
cabbage (Spathyema). 

The duckweed family (Lemnaceae). (Examples: Lemna, 
Spirodela, Wolma. See paragraphs 51-53.) 

946. Order Xyridales, from the genus Xyris, the yellow- 
eyed grass family (Xyridaceae) . Species mostly tropical, but 
a few in North America. Other examples are the pipewort 
family (Eriocaulaceae, example, Eriocaulon septangulare) , the 
pineapple family (Bromeliaceae, example, the pineapple culti- 
vated in Florida) ; the Florida moss or hanging moss (Tillandsia 
usneoides) ; the spiderwort family (Commelinaceae), including 
the spiderwort (Tradescantia, several species in North America) ; 
the pickerel- weed family (Pontederiaceae), including the genus 
Pontederia in borders of ponds and streams. 

947. Order Liliales. — Some of the families are as fol- 
lows: 

The rush family (Juncaceae, example, Juncus), with many 
species, plants of usually swamp habit. 

The lily family (Liliaceae, examples: Lilium, Allium = Onion, 
Erythronium, Yucca). 

The iris family (Iridaceae, examples: Iris, the blue-flag, 
fleur-de-lis, etc.). 



494 CLASSIFICATION. 

The lily-of -the- valley family (Convallariaceae, examples: lily- 
of-the-valley, Trillium, etc.) 

The amaryllis family (Amaryllidaceae, examples: Narcissus, 
the daffodil; Cooperia, in southwestern United States). 

948. Order Scitaminales. — This order includes the large 
showy cultivated Canna of the canna family. 

949. Order Orchidales. Example, the orchid family (Orchi- 
daceae) with Cypripedium, Orchis, etc. 

II. GLASS DICOTYLEDONES. 

Series i. CHORIPETAL^. Petals wanting (Apetalae, or 
Archichlamydae of some authors), or present and distinct from 
one another (Polypetalae, or Metachlamydae). 

950. Order Casuarinales, confined to tropical seacoasts 
(example, Casuarina). 

951. Order Piperales includes the lizard's-tail family (Sau- 
ruraceae), Saururus cernuus, lizard's-tail, in the eastern United 
States. 

952. Order Salicales. — Shrubs or trees, flowers in aments. 
Includes the willows and poplars (Salix and Populus of the 
willow family, Salicaceae. 

953. Order Myricales. — Shrubs or small trees. Includes the 
sweet-gale (Myrica gale) in wet places in northern United States 
and British North America, Myrica cerifera forming thickets 
on sand-dunes along the Atlantic coast, and the sweet-fern 
(Comptonia peregrina = C. asplenifolia) in the eastern United 
States in dry soil of hillsides. 

954. Order Leitneriales. — Shrubs or trees. Includes the cork- 
wood, Leitneria floridana (Leitneriacese). 

955. Order Juglandales. — Trees, staminate flowers in aments. 
The walnut family (Juglandaceae, examples: walnut, butternut, 
etc. Juglans; hickory, Hicoria = Carya. 

956. Order Fagales. — Trees and shrubs. Flowers in aments, 
or the pistillate ones with an involucre which forms a cup in 
fruit, as in the acorn of the oak. 



ORDERS OF ANGIOSPERMS. 495 

The birch family (Betulaceae, examples: Betula, birch; Cory- 
lus, hazelnut; Alnus, alder, etc.). 

The beech family (Fagaceas = Cupulif erae, examples: Fagus, 
beech; Castanea, chestnut; Quercus, oak. 

957. Order Urticales. — Trees, shrubs, or herbs. Examples: 
the elm family (Ulmaceae), the mulberry family (Moraceae), and 
the nettle family (Urticaceae). 

958. Order Santalales, herbs or shrubs, mostly parasitic. 
The mistletoe family (Loranthaceae) , with the American 

mistletoe (Phoradendron flavescens), parasitic on deciduous 
trees in the South Atlantic, Central, and Gulf States (N. J. 
to Ind. Ter.). 

The sandalwood family (Santalaceae, example, the bastard 
toad- flax, Comandra umbellata), widely distributed in North 
America. 

959. Order Aristolochiales. — Herbs or vines with heart- 
shaped or kidney-shaped leaves. The birthwort family (Aris- 
tolochiaceae, example, Aristolochia serpentaria, the Virginia 
snake-root, eastern United States; wild ginger, or heart-leaf, 
Asarum canadense, eastern North America.) 

960. Order Polygonales. — Examples: the buckwheat family 
(Polygonaceae) , including buckwheat (Fagopyrum), and numer- 
ous species of Polygonum, known as smartweed, water-pepper, 
tear-thumb, bindweed, knotweed, prince's-feather, etc. 

961. Order Chenopodiales. — Herbs. There are several fam- 
ilies; one of the largest is the goosefoot family (Chenopodiaceae). 
The genus Chenopodium includes many species, known as goose- 
foot, lamb's-quarters, etc. Here belong also the Russian thistle 
(Salsola tragus) and the saltwort (S. kali). The former is some- 
times a troublesome weed in the central and western United States, 
naturalized from Europe. The latter occurs along the Atlantic 
coast on seabeaches. Atriplex occurs in salty or alkaline soil, 
also the glasswort (Salicornia herbacea), the bugseed (Cori- 
spermum). The pokeweed family (Phytolaccaceae) , the Amaranth 
family (Amaranthaceae), the purslane family (Portulacaceae, 
including the purslane or "pursley," Portulaca oleracea, and 



49^ CLASSIFICA TION. 

the spring-beauty, Claytonia virginica), and the pink family 
(Caryophyllaceae), belong here. 

962. Order Ranales .— Herbs, shrubs, or trees. Examples are: 
The water-lily family (Nymphaeaceae) , with the yellow water-lily 

(Nymphaea advena=Nuphar advena) and the white water-lily 
(Castalia odorata= Nymphaea odorata). 

The magnolia family (Magnoliaceae) , including the mag- 
nolias (Magnolia) and the tulip-tree (Liriodendron) . The crow- 
foot family (Ranunculaceae) , with the buttercups, hepatica, clem- 
atis, etc. 

963. Order Papaverales. — Mostly herbs. Examples are: 
The poppy family (Papaveraceae) , including the opium or 

garden poppy (Papaver somniferum), the blood-root (Sangui- 
naria canadensis), the Dutchman' s-breeches (Bicuculla cucul- 
laria = Dicentra cucullaria), squirrel's-corn (Bicuculla canaden- 
sis =D. canadensis). 

The mustard family (Cruciferae), including the toothwort 
(Dentaria), shepherd's-purse (Bursa bursa-pastoris = Capsella 
bursa-pastoris, the cabbage, turnip, etc. 

964. Order Sarraceniales. — Insectivorous plants. 

The pitcher-plant family (Sarraceniaceae). Examples: Sarra- 
cenia purpurea, the pitcher-plant, in peat-bogs, northern and 
eastern North America. 

The sundew family (Droseraceae) . Examples: Drosera rotun- 
difolia, and other sundews. 

965. Order Rosales. — Herbs, shrubs or trees. Seventeen 
families are given in the eastern United States. Examples: 

The riverweed family (Podostemaceae) , containing the river- 
weed (Podostemon). 

The saxifrage family (Saxifragaceae), containing a number of 
species. Example, Saxifraga virginiensis. 

The gooseberry family (Grossulariaceae), including the wild 
and the cultivated gooseberry. 

The witch-hazel family (Hamamelidaceae) , including the 
witch-hazel (Hamamelis), in eastern North America, and the 
sweet-gum (Liquidambar styracirlua). 



ORDERS OF ANGIOSPERMS. 49/ 

The plane-tree family (Platanaceae) , with the plane-tree, or 
buttonwood (Platanus occidentalis), eastern North America. 
(Other species occur in western United States.) 

The rose family (Rosaceae), including roses, spiraeas, rasp- 
berries, strawberries, the shrubby cinquefoil (Dasiphora fruti- 
cosa), etc. 

The apple family (Pomaceae), including the apple, mountain- 
ash, pear, June-berry (or shadbush, also service-berry), the haw- 
thorns (Crataegus). 

The plum family (Drupaceae), including the cherries, plums, 
peaches, etc. 

The pea family (Papilionaceae) , including the pea, bean, 
clover, vetch, lupine, etc., a very large family. 

966. Order Geraniales. — Herbs, shrubs, or trees. Nine 
families in the eastern United States. Examples: 

The geranium family (Geraniaceae), with the cranesbill (Gera- 
nium maculatum) and others. 

The wood-sorrel family (Oxalidaceae), with the wood-sorrel 
(Oxalis acetosella) and others. 

The flax family (Linaceae). Example, flax (Linum vul- 
garis). 

The spurge family (Euphorbiaceae) . Plants with a milky 
juice, and curious, degenerate flowers. Examples: the castor- 
oil plant (Ricinus), the spurges (many species of Euphorbia). 

967. Order Sapindales. — Mostly trees or shrubs. Twelve 
families in the eastern United States. Example : 

The sumac family (Anacardiaceae) , containing the sumacs in 
the genus Rhus. (Examples: the poison-ivy (R. radicans), a 
climbing vine, in thickets and along fences, in eastern United 
States. Sometimes trained over porches. The poison - oak 
(R. toxicodendron), a low shrub. Poison-sumac or poison-alder 
(R. vernix=R. venenata), sometimes called "thunderwood," 
or dogwood, is a large shrub or small tree, very poisonous. The 
smoke-tree (Cotinus cotinoides) belongs to the same family, and 
is often planted as an ornamental tree. The maple family (Ace- 
raceae), including the maples (Acer). 



49$ CLASSIFICATION. 

The buckeye family (Hippocastanaceae), including the horse- 
chestnut (^Esculus hippocastanum), much planted as a shade 
tree along streets. Also there are several species of buckeye in 
the same genus. 

The jewelweed family (Balsaminaceae), including the touch- 
me-not (Impatiens biflora and aurea) in moist places. The 
garden balsam (Imp. balsamea) also belongs here. 

968. Order Rhamnales. — Shrubs, vines, or small trees. There 
are two families, the buckthorn (Rhamnaceae) , the grape family 
(Vitaceae), including the grapes (Vitis), the American ivy (Par- 
thenocissus quinquefolia=Ampelopsis quinquef olia) , in woods 
and thickets, eastern North America, and much planted as a 
trailer over porches. The Japanese ivy (P. tricuspidata = A. 
veitchii) used as a trailer on the sides of buildings belongs 
here. 

969. Order Malvales. — Herbs, shrubs, or trees. 

The linden family (Tiliaceae). Example, the basswood or 
American linden (Tilia americana.) 

The mallow family (Malvaceae), including the hollyhock, the 
mallows, rose of Sharon (Hibiscus), etc. 

970. Order Parietales, with seven families in the eastern 
United States. The St.-John's-wort (Hypericum) and the vio- 
lets each represent a family. The violets (Violaceae) are well- 
known flowers. 

971. Order Opuntiales. — These include the cacti (Cactaceas), 
chiefly growing in the dry or desert regions of America. 

972. Order Thymeleales, with two families and few 
species. 

973. Order Myrtales. — Land, marsh, or aquatic plants. 
The most conspicuous are in the evening primrose family 
(Onagraceae) , including the fireweeds, or willow herbs (Epilobium), 
and the evening primrose (Onagra biennis = (Enothera bien- 
nis). 

974. Order Umbellales. — Herbs, shrubs, or trees, flowers in 
umbels. 

The ginseng family (Araliaceae) . This includes the spikenards 



ORDERS OF ANGIOSPERMS. 499 

and sarsaparillas in the genus Aralia, and the ginseng (or " sang"), 
Panax quinquefolium. 

The carrot family (Umbellif erae) . This family includes the 
wild carrot (Daucus carota), the poison-hemlock (Cicuta), the 
cultivated carrot and parsnip, and a large number of other genera 
and species. 

The dogwood family (Cornaceae). The flowering dogwood 
(Cornus florida), abundant in eastern North America, is an 
example. 

Series 2. GAMOPETAL.E ( = S'ympetalae or Metachla- 
mydae) . Petals partly or wholly united, rarely separate or wanting. 

975. Order Ericales. — There are six families in eastern 
United States. Examples: 

The wintergreen family (Pyrolaceae) , including the shin-leaf 
(Pyrola elliptica). 

The Indian-pipe family (Monotropacese), with the Indian- 
pipe (Monotropa uniflora) and other humus saprophytes. (See 
paragraphs 182-191.) 

The heath family (Ericaceae). Examples: Labrador tea 
(Ledum), in bogs and swamps in northern North America. 
The azaleas, with several species widely distributed, are beauti- 
ful flowering shrubs, and many varieties are cultivated. The 
rhododendrons are larger with larger flower-clusters, also beau- 
tiful flowering shrubs. R. maximum in the Alleghany Moun- 
tains and vicinity, from Nova Scotia to Ohio and Georgia. R. 
catawbiense, usually at somewhat higher elevations, Virginia 
to Georgia. The mountain laurel (Kalmia latifolia) and 
other species rival the rhododendrons and azaleas in beauty. 
The trailing arbutus (Epigaea repens) in sandy or rocky woods is 
a well-known small trailing shrub in eastern North America. 
The sourwood (Oxydendrum arboreum) is a tree with white 
racemes of flowers in August, and scarlet leaves in autumn. 
The spring or creeping wintergreen (Gaultheria procumbens) is 
a small shrub with aromatic leaves, and bright red spicy berries. 

The huckleberry family (Vaccinaceae) includes the huckle- 
berries (example, Gaylussacia resinosa, the black or high- 



500 CLASSIFICATION. 

bush huckleberry, eastern United States), the mountain cran- 
berry (Vitis-Idaea vitisidaea=Vaccinium vitisidaea) in the north- 
ern hemisphere; the bilberries and blueberries (of genus Vacci- 
nium) ; the cranberries (examples : the large American cranberry, 
Oxycoccus macrocarpus and the European cranberry, Oxycoc- 
cus oxycoccus, in cold bogs of northern North America, the 
latter also in Europe and Asia). 

976. Order Primulales. — Two families here. The primrose 
family (Primulaceae) contains the loosestrifes (Steironema), star- 
flower (Trientalis), etc. 

977. Order Ebenales. — Of the four families, the ebony fam- 
ily (Ebenaceae) contains the well-known persimmon (Diospyros 
virginiana) and the storax family (Styracaceae) with the silver- 
bell, or snowdrop tree (Mohrodendron carolinum). 

978. Order Gentianales. — Herbs, shrubs, vines, or trees. 
Six families in the United States. 

The olive family (Oleaceae) includes the common lilac (Syrin- 
ga), the ash trees (Fraxinus), the privet (Ligustrum). 

The gentian family (Gentianaceae) among other genera in- 
cludes the gentians (Gentiana). 

The milkweed family (Asclepiadaceae) contains plants mostly 
with a milky juice. Asclepias with many species is one of the 
most prominent genera. 

979. Order Polemoniales. — Mostly herbs, rarely shrubs and 
trees. Fifteen families in the eastern United States. 

The morning-glory family (Convolvulaceae) includes the 
bindweeds (Convolvulus), the morning-glory (Ipomaea), etc. 

The dodder family (Cuscutaceae) includes the dodders, or 
" love-vines." There are nearly thirty species in the United 
States. The stems are slender and twine around other plants 
upon which they are parasitic (see paragraph 179). 

The phlox family (Polemoniaceae). The most prominent 
genus is Phlox. Over forty species occur in North America. 

The borage family (Boraginaceae) includes the heliotrope 
(Heliotropium), the hound's-tongue (Cynoglossum), the forget- 
me-not (Myosotis), and others. 



ORDERS OF ANGIOSPERMS. S 01 

The vervain family (verbenaceae) contains the verbenas. 
The mint family (Labiatae) contains the mints (Mentha), skull- 
cap (Scutellaria), dead-nettles (Lamium). 

The potato family (Solanaceae) includes the ground-cherry 
(Physalis), the nightshades (Solanum), the tomato (Lycoper- 
sicon), tobacco (Nicotiana). 

The figwort family (Scrophulariaceae) includes the common 
mullein (Verbascum), the monkey-flower (Mimulus), the toad- 
flax (Linaria), turtle's-head (Chelone), and many other genera 
and species. 

The bladderwort family (Lentibulariaceae) includes the curi- 
ous bog or aquatic plants with finely dissected leaves, and with 
bladders in which insects are caught (Utricularia). 

The trumpet-creeper family (Bignoniaceae) includes the trum- 
pet-creeper (Bignonia), the catalpa tree, and others. 

980. Order Plantaginales with one family (Plantaginaceae) 
includes the plantains (Plantago). 

981. Order Rubiales with three families is represented by 
The madder family (Rubiaceae) with the bluets (Houstonia), 

the button-bush (Cephalanthus), the partridge-berry (Mitchella), 
the bedstraws (Galium), etc. 

The honeysuckle family (Caprifoliaceae) with the elder (Sam- 
bucus), the arrowwoods and cranberry trees (Viburnum), the 
honeysuckles (Lonicera), etc. 

982. Order Valerianates with two families includes 

The teasel family (Dipsacaceae) . Example, Fuller's teasel 
(Dipsacus). 

983. Order Campanulales with five families, the corolla 
usually gamopetalous. 

The gourd family (Cucurbitaceae) includes the pumpkin, 
squash, melon, and a few feral species. Example, the star- 
cucumber (Sicyos angulatus), in moist places in eastern and 
middle United States. 

The bell-flower family (Campanulaceae) includes the hare- 
bells or bell-flowers (Campanula), the lobelias (example, Lobelia 
cardinalis, the cardinal-flower), etc. 



5 02 CLA SSIF1CA TION. 

The chicory family (Cichoriaceae) includes the chicory or 
succory (Cichorium intybus, known also as blue-sailors), the 
oyster-plant or salsify (Tragopogon porrif olius) , the dandelion 
(Taraxacum taraxacum =T. densleonis), the lettuce (Lactuca), 
the hawkweed (Hieraceum), and others. 

The ragweed family (Ambrosiaceae) includes the ragweeds 
(Ambrosia), the cockle-bur (Xanthium), and others. 

The thistle family (Composite) includes the thistle (Carduus), 
asters (Aster), goldenrods (Solidago), sunflowers (Helianthus) , 
eupatoriums or joepye-weeds, thorough worts (Eupatorium) , 
cone-flowers or black-eyed Susans (Rudbeckia), tickseed (Core- 
opsis), bur-marigold or beggar-ticks or devil's-bootjack (Bidens), 
chrysanthemums, etc. 



INDEX. 



Absorption, 13, 22-28 

Aceraceae, 497 

Acorn, 451 

Acorus, 493 

iEcidiomycetes, 218 

^Ecidiospore, 189 

^Esculus hippocastanum, 498 

Agaricaceae, 199, 219 

Agaricus arvensis, 206 

Agaricus campestris, 200-207 

Akene, 451 

Albumen, 98 

Albuminous, 98, 108 

Alder, 495 

Algae, 136-176 

Algae, absorption by, 22 

Alismaceae, 493 

Alpine formation, 474 

A) pine plant societies, 483 

Amanita phalloides, 207, 208 

Amaranth, 495 

Amaryllidaceae, 494 

Aments, 429 

American mistletoe, 495 

Ampelopsis, 498 

Ancylistales, 215 

Andreales, 249 

Andrcecium, 319, 419 

Anemophilous, 435 

Angiosperms, morphology of, 318- 

348; classification, 487 
Antheridiophore, 227 
Antheridium, 144, 149, 155, 176, 223, 

228, 240, 245, 246, 266, 287, 433 
Anthesis, 429 
Anthoceros, 240, 241 
Anthocerotales, 242 
Anthocerotes, 242 
Apogamy, 346 
Apogcotropic (ap"o-ge"o-trop'ic) , 

126 



Apogeotropism (ap"o-ge-ot'ropism) , 

126 
Apple, 456, 497 
Apple family, 497 
Aquatic formations, 475 
Aquatic plant societies, 486 
Araceae, 493 
Archegonia (ar-che-go'ni-a), 223, 

22 9. 233, 241, 244-246, 267, 288, 

20i> 307, 3° 8 
Archegoniophore, 229 
Archegonium, 433 
Archesporium (ar"che-spo'ri-um), 

235 
Archidiales, 249 
Arctic formation, 481 
Aril, 457 
Arisaema, 493 

Arisaema triphyllum, 442, 443 
Aristolochiales, 705 
Arrow leaf, 492 
Arum family, 493 
Asclepias, 500 
Asclepias cornuti, 462 
Ascomycetes (as-co-my-ce'tes), 195- 

198, 216-218 
Ascus, 190, 213 
Ash of plants, 79, 80 
Ash tree, 500 

Aspidium acrostichoides, 253, 257 
Assimilation, 67, 109 
Aster, 502 
Atriplex, 495 
Auriculariales, 218 
Autotrophic plants, 85 
Azalea, 499 
Azolla, 296 

Bacteria, 164, 165 

Bacteria, nitrite and nitrate, 83 

Bacteriales, 164, 165 

5°3 



504 



INDEX. 



Bacteroid, 93 

Bangiales, 175 

Basidiomycetes (ba-sid"i-o-my-ce'- 

tes), 199-208, 218 
Basidium, 201, 213 
Bast, 50-52 

Batrachospermum, 1 71-173, 175 
Bazzania, 25 
Beard-grasses, 480 
Bedstraws, 501 
Beechnut, 452 

Beet, osmose in, 15, 16, 17, 18 
Begonia, 407 
Bellflower, 501 
Berry, 454, 455, 456 
Betulaceae, 495 
Bicuculla, 496 
Bidens, 458 
Bignonia, 501 
Bilberries, 500 
Biotic factors, 466 
Birch, 495 

Bird's-nest fungi, 220 
Blackberry, 454 
Black fungi, 198 
Bladderwort, 501 
Blasia, 164, 236 
Bloodroot, 496 
Bluets, 436, 437, 501 
Boletus, 209 
Boletus edulis, 209 
Boraginaceae, 500 
Botrychium, 295 
Botrydiaceae, 162 
Botrydium granulatum, 146, 162 
Broom sedge, 480 
Brown algas, 167-170 
Bryales, 349 
Buds, winter condition of, 374- 

377 
Buckeye family, 498 
Buckthorn, 498 
Buckwheat, 495 
Buffalo-grass, 480 
Bug seed, 495 
Bulb, 372 

Bunch-grasses, 480 
Butternut, 452, 494 
Buttonbush, 501 
Button wood, 497 

Cacti, 395, 498 
Callithamnion, 173 
Calyptrogen, 361 



Cambium, 50, 52, 358, 363 
Campanula rotundifolia, 442, /\/ \/\ f 

Campanulales, 501 
Canna, 445-449, 494 
Capsella bursa-pastoris, 496 
Capsule, 453 

Carbohydrate, 71, 75, 80, 90 
Carbon dioxide, 62-67, 110-113 
Cardinal flower, 501 
Carpogonium, 172, 176 
Carrot family, 799 
Caryophyllaceae, 496 
■ Caryopsis, 451 
Cassia marilandica, 402 
Cassiope, 395 
Castalia odorata, 496 
Castor-oil plant, 497 
Catalpa, 501 
Catkin, 428 
Cattail-flag, 492 
Caulidium, 371 
Cedar apples, 194 
Cell, 3; artificial 20 
Cell sap, 3, 40 

Ceratopteris thalictroides, 296 
Chaetophora, 151, 162 
Chaetophoraceae, 162 
Chara, 176 
Charales, 176 

Chemical condition of soil, 466 
Chemosynthetic assimilation, 109 
Chenopodiales, 495 
Chenopods, 495 
Chestnut, 452, 494 
Chicory family, 502 
Chlamydomonas, 159, 160 
Chlamydospores, 180 
Chloral hydrate, 65, 87 
Chlorophyceae, 158 
Chlorophyll, 2, 67, 72 
Chloroplast, 68, 69, 71 
Christmas fern, 251-253 
Chromoplast, 71 
Chromosomes, 342-345 
Chroococcaceae, 163 
Chrysanthemum, 502 
Chytridiales, 215 
Cichoriaceae, 502 
Cichorium intybus, 502 
Clavaria botrytes, 212 
Clavariaceae, 210, 219 
Claytonia virginica, 496 
Cleistogamous, 435 



INDEX. 



505 



Clematis virginiana, 462, 463, 706 

Climatic factors, 466 

Climatic formations, 470 

Clostridium pasteurianum, 93 

Clover, 497 

Club mosses, 284, 289 

Coccogonales, 163 

Cocklebur, 502 

Cold wastes, 474 

Coleochaetaceae, 162 

Coleochaste, 153-156, 226 

Collenchyma, 356, 363 

Comandra, 495 

Compass plants, 409 

Compositae, 502 

Comptonia asplenifolia, 494 

Cone fruit, 456 

Confervoideae, 162 

Coniferae, 316 

Conjugation, 137, 141, 160, 162, 

179 
Convallariaceae, 494 
Cooperia, 494 
Cordyceps, 218 
Coreopsis, 502 
Cork, 357, 363 
Corm, 373 
Cortex, 50 
Corymb, 427 
Cotyledon, 99-101 
Cranberry, 500 
Crataegus, 497 
Crowfoot family, 496 
Cruciferae, 496 
Cryptonemiales, 175 
Cucurbitaceae, 501 
Culture formations, 470, 475 
Cultures, water, 28, 29 
Cup fungi, 199 
Cupuliferae, 495 
Cuscuta, 83, 500 
Cushion type of vegetation, 483 
Cuticle, 43 
Cyanophyceae, 163 
Cyatheaceae, 295 
Cycadales, 316 
Cycas,3ii, 312, 457 
Cyclosis, 9, 10 
Cyclosporales, 171 
Cyme, 430, 432 
Cyperaceas, 493 
Cypripedium, 443, 447, 494 
Cystocarp, 174 
Cystopteris bulbifera, 260 



Cystopus, 215 

Cytase, 92, 108 

Cytisus, 445 

Cytoplasm (cy'to-plasm), 5 

Dacryomycetales, 219 

Dahlia, 108 

Dandelion, 502 

Dasiphora fruticosa, 497 

Daucus carota, 499 

Dehiscence, 453 

Dentaria, 322-324 

Dentaria diphylla, 496 

Dermatogen, 359 

Desert formation, 473 

Desert societies, 480 

Desmodium, 458 

Desmodium gyrans, 399 

Diadelphous (di"a-del'phous), 

425 
Diageotropism (di"a-ge-ot'ro-pism) , 

126 
Diahelio tropic (di"a-he"li-o-trop'- 

ic), 127 
Diaheliotropism (di"a-he"li-ot'ro- 

pism), 127 
Diastase, 77, 78, 108, 116 
Diatoms, 166 
Dichogamous (di-chog'a-mous), 437, 

442 
Dicentra, 496 
Dicotyledons, 494 
Dictyophora, 219 
Diffusion, 13-20 
Digestion, 107, 108, 109 
Dimorphism of ferns, 273-280 
Dioecious, 435' 
Dionaea muscipula, 133 
Dipodascus, 216 
Dipsacus, 501 
Discomycetes, 217 
Dodder, 83, 84, 500 
Dogwood, 499 
Dothidiales, 218 
Downy mildews, 185 
Drosera rotundifolia, 133, 496 
Drupaceae, 497 
Drupe, 454 
Duckweeds, 26, 28 
Dudresnaya, 175 
Dunes, 484 

Ebenales, 500 
Ecological factors, 464 



506 



INDEX. 



Ecology (sometimes Written cecol- 

ogy), 464 
Ectocarpus, 167 
Edaphic formations, 475 
Elaphomyces, 217, 218 
Elder, 501 
Elm family, 495 
Elodea, 61-63 
Embryo of ferns, 269-272 
Embryo sac, 326-328 
Empusa, 215 
Endocarp, 450 
Endomyces, 216 
Endosperm, 103, 105, 107, 306, 309; 

nucleus, 327, 329-334 
Entomophthorales, 215 
Enzyme, 92, 98, 116, 117 
Epidermal system, 358 
Epidermis, 358, 359, 363 
Epigsea repens, 499 
Epigynous, 425 
Epilobium, 498 
Epinastic (ep-i-nas'tic), 129 
Epinasty (ep'i-nas-ty), 129 
Epipactis, 444, 447 
Epiphegus, 84 
Epiphytes, 416 
Equisetales, 296 
Equisetineae, 296 
Equisetum, 280-283 
Ericaceae, 499 
Ericales, 499 
Erythronium, 493 
Etiolated plants (e'ti-o-la"ted), 68 
Euascomycetes, 217 
Eubasidiomycetes, 219 
Eupatorium, 403, 502 
Euphorbiacese, 497 
Eurotium oryzae, 78 
Evening primrose family, 498 
Exalbuminous, 108 
Exoascus, 217 
Exobasidiales, 219 
Exocarp, 450 

Fagales, 494 

Fehling's solution, 75, 76 

Ferment, 98, 108, 116 

Ferns, 251-279, 292, 457; classifica- 
tion of, 295 

Fertilization, 307, 308, 328, 329, 140, 
145, 169, 172, 174, 197, 421 

Fibrovascular bundles, 49-54 

Figwort family, 501 



Filicales, 295 

Filicineae, 295 

Fittonia, 404 

Flagellates, 83, 165 

Flax, 497 

Flower cluster, 419 

Flower, form of, 422; parts 0^419; 

union of parts, 424 
Flowers, arrangements of, 426; 

kinds of, 421 
Follicle, 453 
Forest, formations 471; societies, 

477 

Forests, relation to rainfall, 479 

Fresh-Water societies, 486 

Frond, 352 

Fruit, 450-457; Parts of, 450 

Frullania, 25, 236 

Fucus, 168-170 

Fungi, absorption by, 22; classifica- 
tion of, 213-222 ; nutrition of, 86- 
90; respiration in, 115 

Gametangium (gam"et-an'gi-um), 

140 
Gamete (gam'ete), 138, 139 
Gametophore (gam'et-o-phore), 230, 

248 
Gametophyte (gam'et-o-phyte), 225, 

226, 244, 245, 250, 262, 270, 283, 

292, 294, 305, 314, 317, 336-339. 

340-348, 434 
Gamopetalous (gam"o-pet'a-lous) , 

424 
Gamosepalous (gam-o-sep'a-lous), 

424 
Gas in plants, 60-64 
Gasteromycetes, 219 
Gemmae, 179, 235 
General formations, 470 
Gentian, 500 
Geotropism (ge-ot'ro-pism), 125- 

127, 410 
Geraniaceae, 497 
Geraniales, 497 
Geranium family, 497 
Germ, 459 
Gigartinales, 175 
Gingko, 3 1 3-3 1 5, 457 
Gingkoales, 316 
Ginseng, 499 
Glasswort, 495 
Gleicheniaceas, 295 
Glucose, 108. See sugar. 



INDEX. 



507 



Gne tales, 316 

Gonidia, 118, 143, 172, 174, 178- 

184 
Gonidiangium (go'mid-an'gi-um), 

178 
Gonidium, 213 
Gooseberry, 496 
Goosefoot family, 495 
Gracilaria, 173, 174, 175 
Graminales, 492 
Gramineae, 492 
Grape, 498 
Grass family, 492 
Grassland formation, 471 
Green algae, 158 
Growth, 1 18-124, 380 
Gulf weed, 170 
Gymnosperms, 311, 456 
Gymnosporangium, 194 
Gynoecium, 320, 419, 451, 452 
Gyrocephalus, 219 

Halophytes, 468 

Harpochytrium, 214, 215 

Haustorium, 87, 88 

Hawkweed, 502 

Hawthorn, 497 

Hazelnut, 452, 495 

Head, 428 

Heart leaf, 495 

Heath family, 499 

Heliotrope, 500 

Hefiotropism (he-li-ot'ro-pism), 

127-131, 133, 397 
Helvellales, 217 
Hemiascomycetes, 216 
Hemibasidiomycetes, 218 
Hepaticae, 242 

Heterospory (het"er-os'po-ry), 434 
Heterothallic, 180 
Heterotrophic plants, 85 
Hickory, 494 
Hickory nut, 452 
Hilum, 10 1, 102 
Hippocastanaceae, 498 
Holdfasts, 418 
Hollyhock, 498 
Homothallic, 180 
Honeysuckle, 501 
Hormogonales, 163 
Horse-chestnut, 498 
Horsetails, 280-283 
Houstonia coerulea, 437 
Huckleberry, 499 



Humus saprophytes, 85, 91 
Hybridization, 338 
Hydnaceas, 210, 219 
Hydnum coralloides, 210 
Hydnum repandum, 211 
Hydrocarbon, 75 
Hydrodictyaceae, 161 
Hydrophytes, 468 
Hydropterales, 295 
Hydrotropism (hy-drot'ro'pism), 

133, 134, 412 
Hygrophytes, 468 
Hymeniales, 219 
Hymenogastrales, 219 
Hymenomycetes, 219 
Hymenomycetineae, 219 
Hymenophyllaceae, 295 
Hypericum, 498 
Hypocotyl (hy'po-co"tyl), 101 
Hypocreales, 217 
Hypogenous, 425 
Hyponastic (hy-po-nas'tic), 129 
Hyponasty (hy'po-nas-ty), 129 
Hysteriales, 217 

Impatiens, 498 

Impatiens fulva, 460 

Indian -pipe, 499. 

Indian-turnip, 493 

Indusium, 252 

Inflorescence, 426 

Insectivorous plants, 133, 496 

Integument, 304 

Intramolecular respiration, 113, 114 

Inulase, 108 

Inulin, 108, 417 

Iodine, 65 

Ipomcea, 500 

Iridaceae, 493 

Iris, 493 

Irritability, 125-135 

Isoetales, 296 

Isoetes, 289-291, 292 

Isoetineae, 296 

Ivy, 498 

Jack-in-the-pulpit, 373 
JeWelweed, 498 
Juglandales, 494 
June-berry, 497 
Jungermanniales, 242 

Kalmia latifolia, 444 
Karyokinesis, 341-344 



508 



INDEX. 



Kelps, 1 68 
Kingdom, 492 

Labiatae, 423, 501 

Laboulbeniales, 218 

Labrador tea, 499 

Lactuca canadensis, 460 

Lactuca scariola, 409, 460, 461 

Lagenidium, 214, 215 

Laminaria, 168, 169 

Lamium, 424, 501 

Larch, 367 

Laurel, 499 

Leaf patterns, 404 

Leathesia difformis, 168 

Leaves, form and arrangement, 383- 
391; function of, 387; protective 
modifications of, 392; protective 
positions, 395; reduction of sur- 
face, 394; relation to light, 397; 
structure of, 40-43, 13 J > 39 *> 393 

Legumes, 92, 93, 453 

Leguminosae (=Papilionaceae), 396, 

399 
Leitneria floridana, 494 
Leitneriales, 494 
Lemanea, 171, 173, 175, 492 
Lemna, 418 
Lemna trisulca, 26, 27 
Lenticel, 357, 358 
Lepiota naucina, 208 
Lettuce, 502 
Leucoplast, 71 
Lichens, 86, 93-95, 220, 221 
Light, 465 
Liliaceas, 490, 493 
Liliales, 490, 493 
Lilium, 489-493 
Linaria vulgaris, 501 
Linden, 498 
Linum vulgaris, 497 
Lipase, 108 
Liquidambar, 496 
Liriodendron, 496 
Live-forever, 394 
Liverworts, 222-239; absorption by, 

23-25; classification of, 242 
Lobelia, 501 
Lupinus perennis, 353 
Lycoperdales, 220 
Lycopodiaceae, 296 
Lycopodiales, 296 
Lycopodiineae, 296 
Lycopodium, 284-286 



Macrosporangium, 94, 302, 304, 311. 

312, 321 
Macrospore, 287, 290, 326-328, 434 
Magnolia, 496 
Mallow family, 498 
Malvales, 498 
Maple family, 497 
Marchantia, 24, 226-236 
Marchantiales, 242 
Marine plant societies, 486 
Marratiales, 295 
Marsilia, 370 
Marsiliaceae, 296 
Matoniaceae, 295 
Medicago denticulata, 92 
Medulla, 50 

Members of the flower, 335 
Members of the plant, 349-353 
Meristem, 359 
Mesocarp, 450 
Mesophytes, 467 
Microsporangia, 294, 299 
Microspore, 287, 290, 299, 312, 

435 
Microsporophylls, 299, 320, 420 
Milkweed family, 500 
Mimosa, 132, 396 
Mimulus, 501 
Mint family, 501 
Mistletoe, 84, 495 
Mitchella, 501 
Mixotrophic plants, 85 
Mnium, 243-246 
Molds, nutrition of, 86-90 
Molds, Water, 181 
Monadelphous, 424 
Monoblepharidales, 215 
Monoblepharis, 215 
Monocotyledons, 490, 492 
Monoecious, 435 
Monotropa uniflora, 499 
Morchella, 198, 199 
Morel, 198, 199 
Morning-glories, 500 
Mosaics, 405 
Mosses, 243-248, 457; absorption 

by, 25; classification of, 248 
Mucor, 6, 7, 15, 118, 119, 177-180, 

215 
Mucorales, 215 
Mulberry, 704 
Mullein, 366, 394, 501 
Mushrooms, 199-208 
Mustard family, 496 



INDEX. 



509 



Mutation, $-£> 
Mutualism, 95 
Mycelium, 6, 86-90 
Mycetozoa, 213, 214 
Mycorhiza, 86, 91, 92, 217 
Myosotis, 500 
Myrica cerifera, 494 
Myrica gale, 494 
Myricales, 494 
Myriophyllum, 403 
Myrtales, 498 
Myxobacteriales, 165 
Myxomycetes, 83, 213, 214 

Naiadaceae, 492 

Naiadales, 492 

Naias, 492 

Nemalion, 171, 172, 175 

Nemalionales, 175 

Nettle, 495 

Nicotiana, 501 

Nidulariales, 220 

Nitella, 8, 9, 176 

Nitrobacter, 8^ 

Nitrogen, 92, 93 

Nitromonas, 83 

Nostocaceae, 164 

Nucellus, 304 

Nucleus, 3, 4; morphology of, 340- 

345 
Nuphar advena, 496 
Nutation, 123, 124 
Nymphaea odorata, 496 

Oak, 495 
Oak family, 495 
(Edogoniaceae, 162 
(Edogonium, 147-15 1, 350 
(Enothera biennis, 498 
GEnothera gigas, 338 
(Enothera lamarkiana, 338 
Olpidium, 214, 215 
Onagar biennis, 498 
Onagraceae, 498 

Onoclea sensibilis, 254, 273-278 
Oogonium, 144, 150, 155 
Oomycetes, 214, 215 
Ophioglossales, 295 
Ophioglossum, 295 
Opuntiales, 498 
Orchidaceae, 494 
Orchidales, 494 
Orchids, 442 
Oscillatoriaceae, 163 



Osmosis, 13-20 
Osmundaceae, 295 
Ostrich fern, 279 
Ovule, 302, 321, 334, 421 
Oxalis, 497 
Oxycoccus, 500 
Oxydendrum arboreum, 501 
Oxygen, 63, 110-113 

Palisade cells, 41, 43 
Palmaceae, 493 
Palmales, 493 
Palms, 408 
Pandanales, 492 
Pandanus, 492 
Pandorina, 160, 350 
Panicle, 427 
Papaverales, 496 
Papilionaceae, 423, 497 
Parasites, 83, 84, 86 
Parasitic fungi, nutrition of, 86-90 
Parenchyma, 50, 356, 363 
Parietales, 498 
Parkeriaceae, 296 
Parmelia, 96 
Parthenogenesis, 184 
Partridge berry, 501 
Pea, 497 
Pea family, 497 
Pear, 456 
Pediastrum, 161 
Pellia, 164 
Pellonia, 405 
Peltigcra, 94, 95 
Pepo, 456 
Pericycle, 360 
Peridineae, 166 
Perigynous, 425 
Perisperm, 331, 332 
Perisporiales, 217 
Peronospora, 183, 215 
Peronosporales, 215 
Persimmon, 500 
Pezizales, 217 
Phacidiales, 217 
Phaeophyceae, 167 
Phaeosporales, 171 
Phallales, 219 

Phloem, 50-52, 360, 361, 363 
Phlox family, 500 
Phoradendron flavescens, 495 
Photosynthesis, 67, 68, 70, 117 
Phycomycetes (Phy"co-my-cc'tcs). 
214, 215 



5io 



INDEX. 



Phyllidium, 371 

Phylloclades, 373, 395 

Phyllotaxy, 375, 384 

Physical condition of soil, 465 

Physical factors, 465 

Phytolaccaceae, 495 

Phytomyxa leguminosarum, 92 

Phytophthora, 182, 184, 215 

Pickerel weed, 493 

Pilularia, 296 

Pinales, 216 

Pine, white, 297-310 

Piperales, 494 

Pitcher-plant, 496 

Pith, 50 

Plant-food, sources of, 81 

Plant-formations, 496 

Plant-substance, analysis of, 79, 

80 
Plantaginales, 501 
Plantago, 501 

Plasmo lysis (plas-mol'y-sis), 19 
Plasmopara, 183, 215 
Plectascales, 217 
Plectobasidiales, 220 
Pleurococcaceae, 161 
Pleurococcus, 161 
Plum family, 497 
Plumule, 99 
Podostemon, 496 
Poison-hemlock, 499 
Poison-ivy, 497 
Poison-oak, 497 

Poisonous mushrooms, 207, 208 
Poison-sumac, 497 
PokeWeed, 495 
Polemoneales, 500 
Pollen-grain, 299, 305 
Pollination, 303, 304, 420, 430, 433- 

449 
Pollinium, 420 
Polygonales, 495 
Polygonum, 495 
Polypodiaceae, 296 
Polyporaceae, 209, 219 
Polyporus, 209, 210 
Polyporus mollis, 92 
Polyporus sulphureus, 209 
Pomaceae, 49? 
Pondweeds, 492 
Poppy, 496 
Porella, 237 
Portulaca, 495 
Potamogeton, 492 



Potato, 501 

Powdery mildews, 195-198, 217 

Primrose, 498, 500 

Primula, 438 

Primulales, 500 

Procarp, 172, 174, 175 

Progeotropism (pro"ge-ot'ro-pism), 
126 

Promycelium (pro"my-ce'li-um), 192 

Proterandrous, 441, 442 

Proterandry, 444 

Proterogenous, 441, 442 

Proterogeny, 440 

Prothallium, 265, 287, 288, 291, 292, 
304, 305, 3 11 , 3 2 5> 328, 335, 433, 
434 

Protoascales, 216 

Protoascomycetes, 216 

Protobasidiomycetes, 218 

Protococcoideae, 158, 621 

Protodiscales, 217 

Protomyces, 216 

Protonema (pro"to-ne'ma), 248, 264 

Protoplasm, 1-12, 42-43, 342; move- 
ment of, 7-1 1 

Psilotaceae, 296 

Pteridophytes, 295, 434 

Pteris cretica, 346 

Puccinia, 187 

Puff-balls, 220 

Pumpkin, 501 

Purslane, 495 

Pyrenoid, 2, 3 

Pyrenomycetes, 217 

Pyrola, 499 

Pyxidium, 453 

Quercus, 495 
Quillworts, 289-291 
Quince, 456 

Raceme, 427 

Radicle, 99 

Ragweed, 502 

Rainy-season flora, 481 

Ranales, 496 

Ranunculaceae, 496 

Raspberry, 454, 455 

Red algae, 171, 628; uses of, 175 

Reproduction, 137, 143, 149, 154, 

155, 179, 185, 186 
Respiration, 110-116, 117 
Rhamnales, 498 
Rhizoids, 24-26 



INDEX. 



5" 



Rhizome, 354 

Rhizomorph (rhi'zo-morph), 89 

Rhizophidium, 214, 215 

Rhizopus, 177-180, 215 

Rhododendron, 499 

Rhodomeniales, 175 

Rhodophyceae, 171 

Rhus radicans, 416, 497 

Riccia, 23, 164, 222-226 

Ricinus, 497 

Riverweed, 496 

Root, function of, 410-418 

Root-hairs, absorption by, 19, 30, 

32 
Root-hairs, action on soil, 82 
Root pressure, 33, 34, 45 
Root, structure of, 30, 361 362 
Root tubercles, 92 
Roots, kinds of, 415 
Rosaceae, 497 
Rosales, 496 
Rose family, 497 
Rosette, 405 
Rosette plants, 483 
Rubiales, 501 
Rudbeckia, 502 
Rusts, 187-194 

Salicaceae, 494 
Salix, 494 
Salsify, 502 
Salviniaceae, 296 
Samara, 451 
Sandalwood, 495 
Sanguinaria, 496 
Santalales, 495 
Sap, rise of, 53, 54 
Sapindales, 497 
Saprolegnia, 181-184 
Saprolegniales, 215 
Saprophytes, 83-85 
Sargassum, 170 
Sarraceniales, 496 
Sarsaparilla, 499 
Saxifrage, 496 
Schizaeaceae, 295 
Schizocarp, 451 
Schizomycetes, 164 
Schizophyceas, 163 
Sclerenchyma, 356-357, 361, 363 
Scouring -rush, 282 
Screw-pine, 409, 492 
Scrophulariaceae, 501 
Sedge family, 492 



Seed, dispersal of, 458-463 
Seed plants, 338 
Seed, structure of, 98, 102 
Seedlings, 97-107 
Seeds, 330-334 
Selaginella, 286-288, 292 
Selaginellaceae, 296 
Sensitive fern, 273 
Sensitive plants, 132, 396, 399 
Sexual organs, 144, 147 
Shadbush, 497 
Shepherd's-purse, 496 
Shoot, floral, 419, 432 
Shoots, 353-355; types of, 36- 
373; winter condition of, 374- 

377 
Sieve tissue, 358, 363 
Sieve tubes, 52, 53 
Silique, 453 
Silk -cotton tree, 417 
Silver bell, 500 
Siphoneae, 146, 1(^2 
Skunk's cabbage, 439-442 
Slime molds, 83 
Smoke- ree, 497 
Societies, 475 
Solanum, 501 
Solidago, 502 
Sourwood, 499 
Spadix, 428 
Spartium, 446 
Spathyema foetida, 438, 493 
Spermagonia, 190 
Spermatophytes, ^8 
Sphacelaria, 168 
Sphaerella lacustris, 158, 159 
Sphaerella nivalis, 158; 350 
Sphaeriales, 218 
Sphagnales, 248 
Sphagnum, 164 
Spiderwort, 11, 493 
Spike, 428 

Spirodela polyrhiza, 27 
Spirogyra, 1-5, 13, 14, 60, 72, 136- 

140, 350 
Sporangia, 178-182 
Sporangium, 253-258, 281, 290 
Spores, 225, 256-258, 263, 264, 

281 
Sporocarp, 173 
Sporogonium (spo"ro-go'ni-um), 

224, 231, 233, 234, 237, 238, 239, 

241, 246, 247, 248 
Sporophyll, 274, 281, 292 



512 



INDEX. 



Sporophyte (spo'ro-phyte), 225, 226, 
2 3 2 , 2 34, 237-239, 241, 242, 250, 
261, 268, 270, 283, 292, 294, 314, 

3*5, 3*7, 33 6 ~339, 340-348 434 

Spurge family, 497 

Squash, 501 

Staminodium, 446 

Starch, formation of, 68, 70-74; 
changed to sugar, 77, 78; translo- 
cation of, 73; digestion of, 75 

Stems, types of, 365-373 

Stems, Woody, structure of, 381-382 

Stoma (pi. stomata) (sto'ma-ta), 42- 
44, 46 

Strawberry, 455, 497 

Sugar, test for, 75, 76 

Sumac, 497 

Sundew, 133, 496 

Sunflower, 399-401, 502 

Sweet gum, 496 

Symbiosis, 85, 86, 92-95 

Synergids (syn'er-gids), 327, 330 

Syngencesious, 424 

Synthetic assimilation, 67 

Tape-grass, 493 

Taraxacum densleonis, 502 

Teasel, 501 

Telegraph-plant, 399 

Teleutospore, 188 

Temperature, 134, 135, 465 

Tetrasporaceae, 161 

Tetraspores, 173, 174 

Thallophytes, 352 

Thallus, 352 

Thelephoraceae, 219 

Thistle family, 502 

Thunder wood, 497 

Thyrsus, 427 

Tilia, 498 

Tillandsia, 493 

Tissue, tensions of, 57-59 

Tissues, classification of, 363, 364; 

kinds of, 356-359; organization 

of, 35 6 -362 
Toad -flax, 501 
Tomato, 501 
Tradescantia, 493 
Tragopogon, 502 
Trailing arbutus, 499 
Trametes pini, 90 
Transpiration, 35-46 
Tremellales, 218, 219 
Triadelphous, 425 



Trillium, 318-322, 494 

Trumpet-creeper, 501 

Tuberales, 217 

Tubers, 373 

Tundra, 481 

Turgescence, 14, 15 

Turgor, 20; restoration of, 56, 57 

Typha, 493 

Ulmaceae, 495 
Ulmus americana, 495 
Ulothrix, 162 
Ulotrichaceae, 162 
Ulvaceae, 162 
Umbel, 428 
Umbellales, 498 
Uredinales, 218 
Uredineae, 187-194, 218 
Uredospore, 189 
Uromyces caryophyllinus, 87 
Urticales, 495 
Ustilaginales, 218 
Ustilagineae, 218 
Utricularia, 501 

Vaccinium, 499 
Vacuoles, 7, 8 
Valerianales, 501 
Vallisneria spiralis, 493 
Variation, 338 
Vascular tissue, 358, 363 
Vaucheria, 142-146 
Vaucheriaceae, 162 
Vegetation types, 464 
Venus' flytrap, 133 
Verbascum, 501 
Verbena, 501 
Vessels, 52, 53 
Vetch, 92, 497 
Viburnum, 501 
Vicia sativa, 459 
Viola cucullata, 436 
Violaceae, 498 
Virgin 's-bower, 462, 463 
Viscum album, 84 
Vitaceae, 498 
Volvocaceae, 158 

Walnut, 452, 494 

Water, 465 ; flow of, in plants, 53, 54 

Water-lilies, 496 

Water-plantain, 493 

White pine, 396 

Wild carrot, 499 



INDEX. 



513 



Willow family, 494 

Wind, 471 

Wintergreen, 499; leaf of, 43 

Witch-hazel, 496 

Wolffia, 28 

Woodland formation, 470 

Xerophytes, 467 

Xylem, 50, 52, 360, 361, 363 

Xylogen, 92 

Xyridales, 493 



Yeast, 216; fermentation of, ris, 

116 
Yucca, 480, 493 

Zamia, 313, 316, 457 

Zoogonidia, 143., 149, 178-184 

Zoospore, 149, 154 

Zygomycetes, 215 

Zygospore, 2, 138-140, 157, 160, 179, 

'180 
Zygote (zy'gote), 138, 179 



TWO NOTABLE NATURE BOOKS- 
FERNS 

A Manual for the Northeastern States. By C. E. WATERS, Ph.D. 
(Johns Hopkins). With Analytical Keys Based on the Stalks. 
With over 200 illustrations from original drawings and photographs. 
362 pp. Square 8vo. Boxed. $3.00 net. (By mail, $3.34.) 
A popular, but thoroughly scientific book, including all the 
ferns in the region covered by Britton's Manual. Much infor- 
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MUSHROOMS 

Edible, Poisonous Mushrooms, etc. By Prof. GEO. F. ATKIN- 
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With recipes for cooking by Mrs. S. T. RORER, and 
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BBITTON'S MANUAL OF THE FLORA OF THE 
NORTHERN STATES AND CANADA. 

By Director N. L. Britton of the New York Botanical Garden. 
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A comprehensive manual of over a thousand pages, containing about 4,500 
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CHAMPLIN'S YOUNG FOLKS' 

Cyclopaedia of Natural History 

By J. D. Champlin and F. A. Lucas 
With over 800 illustrations. 725 pp. $2.50 

A whole '-nature library" about animals prepared by experts. 
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... A wonderful exhibition, and the story of each individual is interesting 
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proportions." — Brooklyn Eagle. 

CHAMPLIN'S YOUNG FOLKS' 

Cyclopaedia of Literature and Art 

With 270 illustrations. 604 pp. 8vo. $2.50 

Brief accounts of the great books, buildings, statues, pictures, 
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Earlier Volumes of Champlin's Young Folks' Cyclopaedia. 

With numerous illustrations. 8vo. $2.50 each. 

COMMON THINGS. PERSONS and PLACES. 

GAMES and SPORTS. 

^.*^ 12-page circular, with sample pages of Champlin s Young 
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AMERICAN SCIENCE SERIES 



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Chemistry. Advanced Course. 850 pp. 8vo. 2.80 

College Chemistry, xx + 669 pp. 8vo. 2.00 

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Chemical Experiments. By Prof. Remsen and Dr. W. W. Ran- 
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CHEMISTRY 

Cairns's Quantitative Chemical Analysis 

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CHAMBERLIN & SALISBURY'S 

GEOLOGY 

By Thomas C. Chamberlin and Rollin D. Salisbury, Pro- 
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Vol. I. Geological Processes and their Results, xix -\- 654 

pp. $4.00. 
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present status of the science, and of the spirit which actuates the working 
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a teaching book and I have no doubt that it will at once become the 
standard American text-book on geology. 

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full of new ideas. It is one of the indispensable books for the library of 
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THE METRIC SYSTEM. 




io-centimeter rule. The upper edge is in millimeters, the lowei in centimeters and half 

centimeters. 



Units. 
The Meter, for 

LENGTH 



The most commonly used divisions and multiples. 
Centimeter (cm), i/ioo meter; Millimeter (mm), 
i/iooo meter; Micron (//), i/iooo millimeter. The 
micron is the unit in micrometry. 
Kilometer, iooo meters; used in measuring roads and other 
long distances. 
c C Milligram (rag), i/iooo gram. 
The Gram, for ) Kilogram, iooo grams, used for ordinary masses, like 

WEIGHT | groceries, etc. 

THE LITER, for ( Cubic Centimeter (cc), i/iooo liter. This is more 
CAPACITY .... ( common than the correct form, Milliliter. 
Divisions of the units are indicated by Latin prefixes: deci, I 
i/ioo; milli, i/iooo. 

Multiples are designated by Greek prefixes: deka, 10 times; /*«:/*, 
times; &7*, iooo times; wjr/a, 10,000 times. 

TABLE OF METRIC AND ENGLISH MEASURES. 



centi. 



100 



Meter = 100 centimeters, iooo millimeters, 1,000,000 microns, 39.3704 

m MuTimeter (mm) = iooo microns, 1/10 millimeter, 1/1000 meter, 1/25 inch, 

aP MTc X RON t (/![ (unit of measure in micrometry) = 1/1000 mm, 1/1000000 me- 
ter (0.000039 inch), 1/25000 inch, approximately. 

Inch (in.) = 25.399772 mm (25.4 mm, approx.). 

Liter = iooo milliliters or iooo cubic centimeters, 1 quart (approx.). 

Cubic centimeter (cc or cctm) = 1/1000 liter. 

Fluid ounce (8 fluidrachms) = 29.578 cc (30 cc, approx.). 

Gram = 15 -43 2 grains. 

Kilogram (kilo) = 2.204 avoirdupois pounds (2i pounds, approx.). 

OunJe Avoirdupois (437* grains) = 28.349 grams [ (30 grams, 

Ounce Troy or Apothecaries' (480 grains) = 31. 103 grams ) approx. ). 



TEMPERATURE. 

To change Centigrade to Fahrenheit: (C. X |) +32 = F. For example, to 
find the equivalent of io° Centigrade, C. = io°, (10° X f) + 32 = 5° F 

To change Fahrenheit to Centigrade: (F. - 32°) X f = C. For example to 
reduce 50" Fahrenheit to Centigrade, F. = 50 , and(50°- 32 ) XJ = 10 C.; 
r - 40 Fahrenheit to Centigrade, F. = -40°, (- 4°°- 3 2 ) - - 72 , 

whence 72° X 5 = — 4°° C. 

—From "The Microscope" {by S. H. Gage) by permission. 



NOV 2 1905 



